Programs & Examples On #Lambda

Anonymous functions or closures in programming languages such as Lisp, C#, C++, Lua, Python, Ruby, JavaScript, or Java. (Also, lambda expression.)

Uses of Action delegate in C#

Well one thing you could do is if you have a switch:

switch(SomeEnum)
{
  case SomeEnum.One:
      DoThings(someUser);
      break;
  case SomeEnum.Two:
      DoSomethingElse(someUser);
      break;
}

And with the might power of actions you can turn that switch into a dictionary:

Dictionary<SomeEnum, Action<User>> methodList = 
    new Dictionary<SomeEnum, Action<User>>()

methodList.Add(SomeEnum.One, DoSomething);
methodList.Add(SomeEnum.Two, DoSomethingElse); 

...

methodList[SomeEnum](someUser);

Or you could take this farther:

SomeOtherMethod(Action<User> someMethodToUse, User someUser)
{
    someMethodToUse(someUser);
}  

....

var neededMethod = methodList[SomeEnum];
SomeOtherMethod(neededMethod, someUser);

Just a couple of examples. Of course the more obvious use would be Linq extension methods.

List<object>.RemoveAll - How to create an appropriate Predicate

A predicate in T is a delegate that takes in a T and returns a bool. List<T>.RemoveAll will remove all elements in a list where calling the predicate returns true. The easiest way to supply a simple predicate is usually a lambda expression, but you can also use anonymous methods or actual methods.

{
    List<Vehicle> vehicles;
    // Using a lambda
    vehicles.RemoveAll(vehicle => vehicle.EnquiryID == 123);
    // Using an equivalent anonymous method
    vehicles.RemoveAll(delegate(Vehicle vehicle)
    {
        return vehicle.EnquiryID == 123;
    });
    // Using an equivalent actual method
    vehicles.RemoveAll(VehiclePredicate);
}

private static bool VehiclePredicate(Vehicle vehicle)
{
    return vehicle.EnquiryID == 123;
}

Assignment inside lambda expression in Python

Kind of a messy workaround, but assignment in lambdas is illegal anyway, so it doesn't really matter. You can use the builtin exec() function to run assignment from inside the lambda, such as this example:

>>> val
Traceback (most recent call last):
  File "<pyshell#31>", line 1, in <module>
    val
NameError: name 'val' is not defined
>>> d = lambda: exec('val=True', globals())
>>> d()
>>> val
True

Entityframework Join using join method and lambdas

Generally i prefer the lambda syntax with LINQ, but Join is one example where i prefer the query syntax - purely for readability.

Nonetheless, here is the equivalent of your above query (i think, untested):

var query = db.Categories         // source
   .Join(db.CategoryMaps,         // target
      c => c.CategoryId,          // FK
      cm => cm.ChildCategoryId,   // PK
      (c, cm) => new { Category = c, CategoryMaps = cm }) // project result
   .Select(x => x.Category);  // select result

You might have to fiddle with the projection depending on what you want to return, but that's the jist of it.

forEach loop Java 8 for Map entry set

You can use the following code for your requirement

map.forEach((k,v)->System.out.println("Item : " + k + " Count : " + v));

Explicit Return Type of Lambda

You can explicitly specify the return type of a lambda by using -> Type after the arguments list:

[]() -> Type { }

However, if a lambda has one statement and that statement is a return statement (and it returns an expression), the compiler can deduce the return type from the type of that one returned expression. You have multiple statements in your lambda, so it doesn't deduce the type.

Does Java SE 8 have Pairs or Tuples?

Since Java 9, you can create instances of Map.Entry easier than before:

Entry<Integer, String> pair = Map.entry(1, "a");

Map.entry returns an unmodifiable Entry and forbids nulls.

Using Java 8's Optional with Stream::flatMap

I'd like to promote factory methods for creating helpers for functional APIs:

Optional<R> result = things.stream()
        .flatMap(streamopt(this::resolve))
        .findFirst();

The factory method:

<T, R> Function<T, Stream<R>> streamopt(Function<T, Optional<R>> f) {
    return f.andThen(Optional::stream); // or the J8 alternative:
    // return t -> f.apply(t).map(Stream::of).orElseGet(Stream::empty);
}

Reasoning:

  • As with method references in general, compared to lambda expressions, you can't accidentaly capture a variable from the accessible scope, like:

    t -> streamopt(resolve(o))

  • It's composable, you can e.g. call Function::andThen on the factory method result:

    streamopt(this::resolve).andThen(...)

    Whereas in the case of a lambda, you'd need to cast it first:

    ((Function<T, Stream<R>>) t -> streamopt(resolve(t))).andThen(...)

Sorting a list using Lambda/Linq to objects

You could use reflection to access the property.

public List<Employee> Sort(List<Employee> list, String sortBy, String sortDirection)
{
   PropertyInfo property = list.GetType().GetGenericArguments()[0].
                                GetType().GetProperty(sortBy);

   if (sortDirection == "ASC")
   {
      return list.OrderBy(e => property.GetValue(e, null));
   }
   if (sortDirection == "DESC")
   {
      return list.OrderByDescending(e => property.GetValue(e, null));
   }
   else
   {
      throw new ArgumentOutOfRangeException();
   }
}

Notes

  1. Why do you pass the list by reference?
  2. You should use a enum for the sort direction.
  3. You could get a much cleaner solution if you would pass a lambda expression specifying the property to sort by instead of the property name as a string.
  4. In my example list == null will cause a NullReferenceException, you should catch this case.

Collectors.toMap() keyMapper -- more succinct expression?

We can use an optional merger function also in case of same key collision. For example, If two or more persons have the same getLast() value, we can specify how to merge the values. If we not do this, we could get IllegalStateException. Here is the example to achieve this...

Map<String, Person> map = 
roster
    .stream()
    .collect(
        Collectors.toMap(p -> p.getLast(),
                         p -> p,
                         (person1, person2) -> person1+";"+person2)
    );

Return from lambda forEach() in java

You can also throw an exception:

Note:

For the sake of readability each step of stream should be listed in new line.

players.stream()
       .filter(player -> player.getName().contains(name))
       .findFirst()
       .orElseThrow(MyCustomRuntimeException::new);

if your logic is loosely "exception driven" such as there is one place in your code that catches all exceptions and decides what to do next. Only use exception driven development when you can avoid littering your code base with multiples try-catch and throwing these exceptions are for very special cases that you expect them and can be handled properly.)

Multiple Order By with LINQ

You can use the ThenBy and ThenByDescending extension methods:

foobarList.OrderBy(x => x.Foo).ThenBy( x => x.Bar)

Where do I mark a lambda expression async?

And for those of you using an anonymous expression:

await Task.Run(async () =>
{
   SQLLiteUtils slu = new SQLiteUtils();
   await slu.DeleteGroupAsync(groupname);
});

How do you perform a left outer join using linq extension methods

Whilst the accepted answer works and is good for Linq to Objects it bugged me that the SQL query isn't just a straight Left Outer Join.

The following code relies on the LinkKit Project that allows you to pass expressions and invoke them to your query.

static IQueryable<TResult> LeftOuterJoin<TSource,TInner, TKey, TResult>(
     this IQueryable<TSource> source, 
     IQueryable<TInner> inner, 
     Expression<Func<TSource,TKey>> sourceKey, 
     Expression<Func<TInner,TKey>> innerKey, 
     Expression<Func<TSource, TInner, TResult>> result
    ) {
    return from a in source.AsExpandable()
            join b in inner on sourceKey.Invoke(a) equals innerKey.Invoke(b) into c
            from d in c.DefaultIfEmpty()
            select result.Invoke(a,d);
}

It can be used as follows

Table1.LeftOuterJoin(Table2, x => x.Key1, x => x.Key2, (x,y) => new { x,y});

Java 8 List<V> into Map<K, V>

Most of the answers listed, miss a case when the list has duplicate items. In that case there answer will throw IllegalStateException. Refer the below code to handle list duplicates as well:

public Map<String, Choice> convertListToMap(List<Choice> choices) {
    return choices.stream()
        .collect(Collectors.toMap(Choice::getName, choice -> choice,
            (oldValue, newValue) -> newValue));
  }

Java "lambda expressions not supported at this language level"

Ctrl + Alt + Shift + S and then from project select the language level 1.8, read more about Lambda Expressions here

How to add data to DataGridView

LINQ is a "query" language (thats the Q), so modifying data is outside its scope.

That said, your DataGridView is presumably bound to an ItemsSource, perhaps of type ObservableCollection<T> or similar. In that case, just do something like X.ToList().ForEach(yourGridSource.Add) (this might have to be adapted based on the type of source in your grid).

lambda expression for exists within list

If listOfIds is a list, this will work, but, List.Contains() is a linear search, so this isn't terribly efficient.

You're better off storing the ids you want to look up into a container that is suited for searching, like Set.

List<int> listOfIds = new List(GetListOfIds());
lists.Where(r=>listOfIds.Contains(r.Id));

Is there a reason for C#'s reuse of the variable in a foreach?

The compiler declares the variable in a way that makes it highly prone to an error that is often difficult to find and debug, while producing no perceivable benefits.

Your criticism is entirely justified.

I discuss this problem in detail here:

Closing over the loop variable considered harmful

Is there something you can do with foreach loops this way that you couldn't if they were compiled with an inner-scoped variable? or is this just an arbitrary choice that was made before anonymous methods and lambda expressions were available or common, and which hasn't been revised since then?

The latter. The C# 1.0 specification actually did not say whether the loop variable was inside or outside the loop body, as it made no observable difference. When closure semantics were introduced in C# 2.0, the choice was made to put the loop variable outside the loop, consistent with the "for" loop.

I think it is fair to say that all regret that decision. This is one of the worst "gotchas" in C#, and we are going to take the breaking change to fix it. In C# 5 the foreach loop variable will be logically inside the body of the loop, and therefore closures will get a fresh copy every time.

The for loop will not be changed, and the change will not be "back ported" to previous versions of C#. You should therefore continue to be careful when using this idiom.

Using member variable in lambda capture list inside a member function

An alternate method that limits the scope of the lambda rather than giving it access to the whole this is to pass in a local reference to the member variable, e.g.

auto& localGrid = grid;
int i;
for_each(groups.cbegin(),groups.cend(),[localGrid,&i](pair<int,set<int>> group){
            i++;
            cout<<i<<endl;
   });

How to merge a list of lists with same type of items to a single list of items?

For List<List<List<x>>> and so on, use

list.SelectMany(x => x.SelectMany(y => y)).ToList();

This has been posted in a comment, but it does deserves a separate reply in my opinion.

Can a java lambda have more than 1 parameter?

To make the use of lambda : There are three type of operation:
1. Accept parameter --> Consumer
2. Test parameter return boolean --> Predicate
3. Manipulate parameter and return value --> Function

Java Functional interface upto two parameter:
Single parameter interface
Consumer
Predicate
Function

Two parameter interface
BiConsumer
BiPredicate
BiFunction

For more than two, you have to create functional interface as follow(Consumer type):

@FunctionalInterface
public interface FiveParameterConsumer<T, U, V, W, X> {
    public void accept(T t, U u, V v, W w, X x);
}

Why are Python lambdas useful?

In Python, lambda is just a way of defining functions inline,

a = lambda x: x + 1
print a(1)

and..

def a(x): return x + 1
print a(1)

..are the exact same.

There is nothing you can do with lambda which you cannot do with a regular function—in Python functions are an object just like anything else, and lambdas simply define a function:

>>> a = lambda x: x + 1
>>> type(a)
<type 'function'>

I honestly think the lambda keyword is redundant in Python—I have never had the need to use them (or seen one used where a regular function, a list-comprehension or one of the many builtin functions could have been better used instead)

For a completely random example, from the article "Python’s lambda is broken!":

To see how lambda is broken, try generating a list of functions fs=[f0,...,f9] where fi(n)=i+n. First attempt:

>>> fs = [(lambda n: i + n) for i in range(10)]
>>> fs[3](4)
13

I would argue, even if that did work, it's horribly and "unpythonic", the same functionality could be written in countless other ways, for example:

>>> n = 4
>>> [i + n for i in range(10)]
[4, 5, 6, 7, 8, 9, 10, 11, 12, 13]

Yes, it's not the same, but I have never seen a cause where generating a group of lambda functions in a list has been required. It might make sense in other languages, but Python is not Haskell (or Lisp, or ...)

Please note that we can use lambda and still achieve the desired results in this way :

>>> fs = [(lambda n,i=i: i + n) for i in range(10)]
>>> fs[3](4)
7

Edit:

There are a few cases where lambda is useful, for example it's often convenient when connecting up signals in PyQt applications, like this:

w = PyQt4.QtGui.QLineEdit()
w.textChanged.connect(lambda event: dothing())

Just doing w.textChanged.connect(dothing) would call the dothing method with an extra event argument and cause an error. Using the lambda means we can tidily drop the argument without having to define a wrapping function.

Java 8 lambda get and remove element from list

With Eclipse Collections you can use detectIndex along with remove(int) on any java.util.List.

List<Integer> integers = Lists.mutable.with(1, 2, 3, 4, 5);
int index = Iterate.detectIndex(integers, i -> i > 2);
if (index > -1) {
    integers.remove(index);
}

Assert.assertEquals(Lists.mutable.with(1, 2, 4, 5), integers);

If you use the MutableList type from Eclipse Collections, you can call the detectIndex method directly on the list.

MutableList<Integer> integers = Lists.mutable.with(1, 2, 3, 4, 5);
int index = integers.detectIndex(i -> i > 2);
if (index > -1) {
    integers.remove(index);
}

Assert.assertEquals(Lists.mutable.with(1, 2, 4, 5), integers);

Note: I am a committer for Eclipse Collections

How to check if element exists using a lambda expression?

While the accepted answer is correct, I'll add a more elegant version (in my opinion):

boolean idExists = tabPane.getTabs().stream()
    .map(Tab::getId)
    .anyMatch(idToCheck::equals);

Don't neglect using Stream#map() which allows to flatten the data structure before applying the Predicate.

How to use Lambda in LINQ select statement

using LINQ query expression

 IEnumerable<SelectListItem> stores =
        from store in database.Stores
        where store.CompanyID == curCompany.ID
        select new SelectListItem { Value = store.Name, Text = store.ID };

 ViewBag.storeSelector = stores;

or using LINQ extension methods with lambda expressions

 IEnumerable<SelectListItem> stores = database.Stores
        .Where(store => store.CompanyID == curCompany.ID)
        .Select(store => new SelectListItem { Value = store.Name, Text = store.ID });

 ViewBag.storeSelector = stores;

Java 8 stream map on entry set

Question might be a little dated, but you could simply use AbstractMap.SimpleEntry<> as follows:

private Map<String, AttributeType> mapConfig(
    Map<String, String> input, String prefix) {
       int subLength = prefix.length();
       return input.entrySet()
          .stream()
          .map(e -> new AbstractMap.SimpleEntry<>(
               e.getKey().substring(subLength),
               AttributeType.GetByName(e.getValue()))
          .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

any other Pair-like value object would work too (ie. ApacheCommons Pair tuple).

No Multiline Lambda in Python: Why not?

I am starting with python but coming from Javascript the most obvious way is extract the expression as a function....

Contrived example, multiply expression (x*2) is extracted as function and therefore I can use multiline:

def multiply(x):
  print('I am other line')
  return x*2

r = map(lambda x : multiply(x), [1, 2, 3, 4])
print(list(r))

https://repl.it/@datracka/python-lambda-function

Maybe it does not answer exactly the question if that was how to do multiline in the lambda expression itself, but in case somebody gets this thread looking how to debug the expression (like me) I think it will help

Getting all types that implement an interface

Mine would be this in c# 3.0 :)

var type = typeof(IMyInterface);
var types = AppDomain.CurrentDomain.GetAssemblies()
    .SelectMany(s => s.GetTypes())
    .Where(p => type.IsAssignableFrom(p));

Basically, the least amount of iterations will always be:

loop assemblies  
 loop types  
  see if implemented.

Using GroupBy, Count and Sum in LINQ Lambda Expressions

var boxSummary = from b in boxes
                 group b by b.Owner into g
                 let nrBoxes = g.Count()
                 let totalWeight = g.Sum(w => w.Weight)
                 let totalVolume = g.Sum(v => v.Volume)
                 select new { Owner = g.Key, Boxes = nrBoxes,
                              TotalWeight = totalWeight,
                              TotalVolume = totalVolume }

Fastest way to Remove Duplicate Value from a list<> by lambda

If you want to stick with the original List instead of creating a new one, you can something similar to what the Distinct() extension method does internally, i.e. use a HashSet to check for uniqueness:

HashSet<long> set = new HashSet<long>(longs.Count);
longs.RemoveAll(x => !set.Add(x));

The List class provides this convenient RemoveAll(predicate) method that drops all elements not satisfying the condition specified by the predicate. The predicate is a delegate taking a parameter of the list's element type and returning a bool value. The HashSet's Add() method returns true only if the set doesn't contain the item yet. Thus by removing any items from the list that can't be added to the set you effectively remove all duplicates.

How to use a Java8 lambda to sort a stream in reverse order?

If you want to sort by Object's date type property then

public class Visit implements Serializable, Comparable<Visit>{
private static final long serialVersionUID = 4976278839883192037L;

private Date dos;

public Date getDos() {
    return dos;
}

public void setDos(Date dos) {
    this.dos = dos;
}

@Override
public int compareTo(Visit visit) {
    return this.getDos().compareTo(visit.getDos());
}

}

List<Visit> visits = getResults();//Method making the list
Collections.sort(visits, Collections.reverseOrder());//Reverser order

LINQ: "contains" and a Lambda query

I'm not sure precisely what you're looking for, but this program:

    public class Building
    {
        public enum StatusType
        {
            open,
            closed,
            weird,
        };

        public string Name { get; set; }
        public StatusType Status { get; set; }
    }

    public static List <Building> buildingList = new List<Building> ()
    {
        new Building () { Name = "one", Status = Building.StatusType.open },
        new Building () { Name = "two", Status = Building.StatusType.closed },
        new Building () { Name = "three", Status = Building.StatusType.weird },

        new Building () { Name = "four", Status = Building.StatusType.open },
        new Building () { Name = "five", Status = Building.StatusType.closed },
        new Building () { Name = "six", Status = Building.StatusType.weird },
    };

    static void Main (string [] args)
    {
        var statusList = new List<Building.StatusType> () { Building.StatusType.open, Building.StatusType.closed };

        var q = from building in buildingList
                where statusList.Contains (building.Status)
                select building;

        foreach ( var b in q )
            Console.WriteLine ("{0}: {1}", b.Name, b.Status);
    }

produces the expected output:

one: open
two: closed
four: open
five: closed

This program compares a string representation of the enum and produces the same output:

    public class Building
    {
        public enum StatusType
        {
            open,
            closed,
            weird,
        };

        public string Name { get; set; }
        public string Status { get; set; }
    }

    public static List <Building> buildingList = new List<Building> ()
    {
        new Building () { Name = "one", Status = "open" },
        new Building () { Name = "two", Status = "closed" },
        new Building () { Name = "three", Status = "weird" },

        new Building () { Name = "four", Status = "open" },
        new Building () { Name = "five", Status = "closed" },
        new Building () { Name = "six", Status = "weird" },
    };

    static void Main (string [] args)
    {
        var statusList = new List<Building.StatusType> () { Building.StatusType.open, Building.StatusType.closed };
        var statusStringList = statusList.ConvertAll <string> (st => st.ToString ());

        var q = from building in buildingList
                where statusStringList.Contains (building.Status)
                select building;

        foreach ( var b in q )
            Console.WriteLine ("{0}: {1}", b.Name, b.Status);

        Console.ReadKey ();
    }

I created this extension method to convert one IEnumerable to another, but I'm not sure how efficient it is; it may just create a list behind the scenes.

public static IEnumerable <TResult> ConvertEach (IEnumerable <TSource> sources, Func <TSource,TResult> convert)
{
    foreach ( TSource source in sources )
        yield return convert (source);
}

Then you can change the where clause to:

where statusList.ConvertEach <string> (status => status.GetCharValue()).
    Contains (v.Status)

and skip creating the List<string> with ConvertAll () at the beginning.

Java 8 Lambda Stream forEach with multiple statements

Forgot to relate to the first code snippet. I wouldn't use forEach at all. Since you are collecting the elements of the Stream into a List, it would make more sense to end the Stream processing with collect. Then you would need peek in order to set the ID.

List<Entry> updatedEntries = 
    entryList.stream()
             .peek(e -> e.setTempId(tempId))
             .collect (Collectors.toList());

For the second snippet, forEach can execute multiple expressions, just like any lambda expression can :

entryList.forEach(entry -> {
  if(entry.getA() == null){
    printA();
  }
  if(entry.getB() == null){
    printB();
  }
  if(entry.getC() == null){
    printC();
  }
});

However (looking at your commented attempt), you can't use filter in this scenario, since you will only process some of the entries (for example, the entries for which entry.getA() == null) if you do.

In Java 8 how do I transform a Map<K,V> to another Map<K,V> using a lambda?

Keep it Simple and use Java 8:-

 Map<String, AccountGroupMappingModel> mapAccountGroup=CustomerDAO.getAccountGroupMapping();
 Map<String, AccountGroupMappingModel> mapH2ToBydAccountGroups = 
              mapAccountGroup.entrySet().stream()
                         .collect(Collectors.toMap(e->e.getValue().getH2AccountGroup(),
                                                   e ->e.getValue())
                                  );

What is key=lambda

 >>> sorted(['Some', 'words', 'sort', 'differently'], key=lambda word: word.lower())

Actually, above codes can be:

>>> sorted(['Some','words','sort','differently'],key=str.lower)

According to https://docs.python.org/2/library/functions.html?highlight=sorted#sorted, key specifies a function of one argument that is used to extract a comparison key from each list element: key=str.lower. The default value is None (compare the elements directly).

Distinct() with lambda?

All solutions I've seen here rely on selecting an already comparable field. If one needs to compare in a different way, though, this solution here seems to work generally, for something like:

somedoubles.Distinct(new LambdaComparer<double>((x, y) => Math.Abs(x - y) < double.Epsilon)).Count()

How do I define a method which takes a lambda as a parameter in Java 8?

For anyone who is googling this, a good method would be to use java.util.function.BiConsumer. ex:

Import java.util.function.Consumer
public Class Main {
    public static void runLambda(BiConsumer<Integer, Integer> lambda) {
        lambda.accept(102, 54)
    }

    public static void main(String[] args) {
        runLambda((int1, int2) -> System.out.println(int1 + " + " + int2 + " = " + (int1 + int2)));
    }

The outprint would be: 166

What is a lambda expression in C++11?

The problem

C++ includes useful generic functions like std::for_each and std::transform, which can be very handy. Unfortunately they can also be quite cumbersome to use, particularly if the functor you would like to apply is unique to the particular function.

#include <algorithm>
#include <vector>

namespace {
  struct f {
    void operator()(int) {
      // do something
    }
  };
}

void func(std::vector<int>& v) {
  f f;
  std::for_each(v.begin(), v.end(), f);
}

If you only use f once and in that specific place it seems overkill to be writing a whole class just to do something trivial and one off.

In C++03 you might be tempted to write something like the following, to keep the functor local:

void func2(std::vector<int>& v) {
  struct {
    void operator()(int) {
       // do something
    }
  } f;
  std::for_each(v.begin(), v.end(), f);
}

however this is not allowed, f cannot be passed to a template function in C++03.

The new solution

C++11 introduces lambdas allow you to write an inline, anonymous functor to replace the struct f. For small simple examples this can be cleaner to read (it keeps everything in one place) and potentially simpler to maintain, for example in the simplest form:

void func3(std::vector<int>& v) {
  std::for_each(v.begin(), v.end(), [](int) { /* do something here*/ });
}

Lambda functions are just syntactic sugar for anonymous functors.

Return types

In simple cases the return type of the lambda is deduced for you, e.g.:

void func4(std::vector<double>& v) {
  std::transform(v.begin(), v.end(), v.begin(),
                 [](double d) { return d < 0.00001 ? 0 : d; }
                 );
}

however when you start to write more complex lambdas you will quickly encounter cases where the return type cannot be deduced by the compiler, e.g.:

void func4(std::vector<double>& v) {
    std::transform(v.begin(), v.end(), v.begin(),
        [](double d) {
            if (d < 0.0001) {
                return 0;
            } else {
                return d;
            }
        });
}

To resolve this you are allowed to explicitly specify a return type for a lambda function, using -> T:

void func4(std::vector<double>& v) {
    std::transform(v.begin(), v.end(), v.begin(),
        [](double d) -> double {
            if (d < 0.0001) {
                return 0;
            } else {
                return d;
            }
        });
}

"Capturing" variables

So far we've not used anything other than what was passed to the lambda within it, but we can also use other variables, within the lambda. If you want to access other variables you can use the capture clause (the [] of the expression), which has so far been unused in these examples, e.g.:

void func5(std::vector<double>& v, const double& epsilon) {
    std::transform(v.begin(), v.end(), v.begin(),
        [epsilon](double d) -> double {
            if (d < epsilon) {
                return 0;
            } else {
                return d;
            }
        });
}

You can capture by both reference and value, which you can specify using & and = respectively:

  • [&epsilon] capture by reference
  • [&] captures all variables used in the lambda by reference
  • [=] captures all variables used in the lambda by value
  • [&, epsilon] captures variables like with [&], but epsilon by value
  • [=, &epsilon] captures variables like with [=], but epsilon by reference

The generated operator() is const by default, with the implication that captures will be const when you access them by default. This has the effect that each call with the same input would produce the same result, however you can mark the lambda as mutable to request that the operator() that is produced is not const.

What is a lambda (function)?

I like the explanation of Lambdas in this article: The Evolution Of LINQ And Its Impact On The Design Of C#. It made a lot of sense to me as it shows a real world for Lambdas and builds it out as a practical example.

Their quick explanation: Lambdas are a way to treat code (functions) as data.

How can I throw CHECKED exceptions from inside Java 8 streams?

The simple answer to your question is: You can't, at least not directly. And it's not your fault. Oracle messed it up. They cling on the concept of checked exceptions, but inconsistently forgot to take care of checked exceptions when designing the functional interfaces, streams, lambda etc. That's all grist to the mill of experts like Robert C. Martin who call checked exceptions a failed experiment.

In my opinion, this is a huge bug in the API and a minor bug in the language specification.

The bug in the API is that it provides no facility for forwarding checked exceptions where this actually would make an awful lot of sense for functional programming. As I will demonstrate below, such a facility would've been easily possible.

The bug in the language specification is that it does not allow a type parameter to infer a list of types instead of a single type as long as the type parameter is only used in situations where a list of types is permissable (throws clause).

Our expectation as Java programmers is that the following code should compile:

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;

public class CheckedStream {
    // List variant to demonstrate what we actually had before refactoring.
    public List<Class> getClasses(final List<String> names) throws ClassNotFoundException {
        final List<Class> classes = new ArrayList<>();
        for (final String name : names)
            classes.add(Class.forName(name));
        return classes;
    }

    // The Stream function which we want to compile.
    public Stream<Class> getClasses(final Stream<String> names) throws ClassNotFoundException {
        return names.map(Class::forName);
    }
}

However, it gives:

cher@armor1:~/playground/Java/checkedStream$ javac CheckedStream.java 
CheckedStream.java:13: error: incompatible thrown types ClassNotFoundException in method reference
        return names.map(Class::forName);
                         ^
1 error

The way in which the functional interfaces are defined currently prevents the Compiler from forwarding the exception - there is no declaration which would tell Stream.map() that if Function.apply() throws E, Stream.map() throws E as well.

What's missing is a declaration of a type parameter for passing through checked exceptions. The following code shows how such a pass-through type parameter actually could have been declared with the current syntax. Except for the special case in the marked line, which is a limit discussed below, this code compiles and behaves as expected.

import java.io.IOException;
interface Function<T, R, E extends Throwable> {
    // Declare you throw E, whatever that is.
    R apply(T t) throws E;
}   

interface Stream<T> {
    // Pass through E, whatever mapper defined for E.
    <R, E extends Throwable> Stream<R> map(Function<? super T, ? extends R, E> mapper) throws E;
}   

class Main {
    public static void main(final String... args) throws ClassNotFoundException {
        final Stream<String> s = null;

        // Works: E is ClassNotFoundException.
        s.map(Class::forName);

        // Works: E is RuntimeException (probably).
        s.map(Main::convertClass);

        // Works: E is ClassNotFoundException.
        s.map(Main::throwSome);

        // Doesn't work: E is Exception.
        s.map(Main::throwSomeMore);  // error: unreported exception Exception; must be caught or declared to be thrown
    }   

    public static Class convertClass(final String s) {
        return Main.class;
    }   

    static class FooException extends ClassNotFoundException {}

    static class BarException extends ClassNotFoundException {}

    public static Class throwSome(final String s) throws FooException, BarException {
        throw new FooException();
    }   

    public static Class throwSomeMore(final String s) throws ClassNotFoundException, IOException  {
        throw new FooException();
    }   
}   

In the case of throwSomeMore we would like to see IOException being missed, but it actually misses Exception.

This is not perfect because type inference seems to be looking for a single type, even in the case of exceptions. Because the type inference needs a single type, E needs to resolve to a common super of ClassNotFoundException and IOException, which is Exception.

A tweak to the definition of type inference is needed so that the compiler would look for multiple types if the type parameter is used where a list of types is permissible (throws clause). Then the exception type reported by the compiler would be as specific as the original throws declaration of the checked exceptions of the referenced method, not a single catch-all super type.

The bad news is that this means that Oracle messed it up. Certainly they won't break user-land code, but introducing exception type parameters to the existing functional interfaces would break compilation of all user-land code that uses these interfaces explicitly. They'll have to invent some new syntax sugar to fix this.

The even worse news is that this topic was already discussed by Brian Goetz in 2010 https://blogs.oracle.com/briangoetz/entry/exception_transparency_in_java (new link: http://mail.openjdk.java.net/pipermail/lambda-dev/2010-June/001484.html) but I'm informed that this investigation ultimately did not pan out, and that there is no current work at Oracle that I know of to mitigate the interactions between checked exceptions and lambdas.

Proper usage of Optional.ifPresent()

Why write complicated code when you could make it simple?

Indeed, if you are absolutely going to use the Optional class, the most simple code is what you have already written ...

if (user.isPresent())
{
    doSomethingWithUser(user.get());
}

This code has the advantages of being

  1. readable
  2. easy to debug (breakpoint)
  3. not tricky

Just because Oracle has added the Optional class in Java 8 doesn't mean that this class must be used in all situation.

Group by with multiple columns using lambda

Further to aduchis answer above - if you then need to filter based on those group by keys, you can define a class to wrap the many keys.

return customers.GroupBy(a => new CustomerGroupingKey(a.Country, a.Gender))
                .Where(a => a.Key.Country == "Ireland" && a.Key.Gender == "M")
                .SelectMany(a => a)
                .ToList();

Where CustomerGroupingKey takes the group keys:

    private class CustomerGroupingKey
    {
        public CustomerGroupingKey(string country, string gender)
        {
            Country = country;
            Gender = gender;
        }

        public string Country { get; }

        public string Gender { get; }
    }

Java 8 optional: ifPresent return object orElseThrow exception

Use the map-function instead. It transforms the value inside the optional.

Like this:

private String getStringIfObjectIsPresent(Optional<Object> object) {
    return object.map(() -> {
        String result = "result";
        //some logic with result and return it
        return result;
    }).orElseThrow(MyCustomException::new);
}

How do I use the new computeIfAbsent function?

Suppose you have the following code:

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class Test {
    public static void main(String[] s) {
        Map<String, Boolean> whoLetDogsOut = new ConcurrentHashMap<>();
        whoLetDogsOut.computeIfAbsent("snoop", k -> f(k));
        whoLetDogsOut.computeIfAbsent("snoop", k -> f(k));
    }
    static boolean f(String s) {
        System.out.println("creating a value for \""+s+'"');
        return s.isEmpty();
    }
}

Then you will see the message creating a value for "snoop" exactly once as on the second invocation of computeIfAbsent there is already a value for that key. The k in the lambda expression k -> f(k) is just a placeolder (parameter) for the key which the map will pass to your lambda for computing the value. So in the example the key is passed to the function invocation.

Alternatively you could write: whoLetDogsOut.computeIfAbsent("snoop", k -> k.isEmpty()); to achieve the same result without a helper method (but you won’t see the debugging output then). And even simpler, as it is a simple delegation to an existing method you could write: whoLetDogsOut.computeIfAbsent("snoop", String::isEmpty); This delegation does not need any parameters to be written.

To be closer to the example in your question, you could write it as whoLetDogsOut.computeIfAbsent("snoop", key -> tryToLetOut(key)); (it doesn’t matter whether you name the parameter k or key). Or write it as whoLetDogsOut.computeIfAbsent("snoop", MyClass::tryToLetOut); if tryToLetOut is static or whoLetDogsOut.computeIfAbsent("snoop", this::tryToLetOut); if tryToLetOut is an instance method.

OrderBy descending in Lambda expression?

As Brannon says, it's OrderByDescending and ThenByDescending:

var query = from person in people
            orderby person.Name descending, person.Age descending
            select person.Name;

is equivalent to:

var query = people.OrderByDescending(person => person.Name)
                  .ThenByDescending(person => person.Age)
                  .Select(person => person.Name);

Python loop for inside lambda

To add on to chepner's answer for Python 3.0 you can alternatively do:

x = lambda x: list(map(print, x))

Of course this is only if you have the means of using Python > 3 in the future... Looks a bit cleaner in my opinion, but it also has a weird return value, but you're probably discarding it anyway.

I'll just leave this here for reference.

List comprehension vs. lambda + filter

An important difference is that list comprehension will return a list while the filter returns a filter, which you cannot manipulate like a list (ie: call len on it, which does not work with the return of filter).

My own self-learning brought me to some similar issue.

That being said, if there is a way to have the resulting list from a filter, a bit like you would do in .NET when you do lst.Where(i => i.something()).ToList(), I am curious to know it.

EDIT: This is the case for Python 3, not 2 (see discussion in comments).

How to map to multiple elements with Java 8 streams?

It's an interesting question, because it shows that there are a lot of different approaches to achieve the same result. Below I show three different implementations.


Default methods in Collection Framework: Java 8 added some methods to the collections classes, that are not directly related to the Stream API. Using these methods, you can significantly simplify the implementation of the non-stream implementation:

Collection<DataSet> convert(List<MultiDataPoint> multiDataPoints) {
    Map<String, DataSet> result = new HashMap<>();
    multiDataPoints.forEach(pt ->
        pt.keyToData.forEach((key, value) ->
            result.computeIfAbsent(
                key, k -> new DataSet(k, new ArrayList<>()))
            .dataPoints.add(new DataPoint(pt.timestamp, value))));
    return result.values();
}

Stream API with flatten and intermediate data structure: The following implementation is almost identical to the solution provided by Stuart Marks. In contrast to his solution, the following implementation uses an anonymous inner class as intermediate data structure.

Collection<DataSet> convert(List<MultiDataPoint> multiDataPoints) {
    return multiDataPoints.stream()
        .flatMap(mdp -> mdp.keyToData.entrySet().stream().map(e ->
            new Object() {
                String key = e.getKey();
                DataPoint dataPoint = new DataPoint(mdp.timestamp, e.getValue());
            }))
        .collect(
            collectingAndThen(
                groupingBy(t -> t.key, mapping(t -> t.dataPoint, toList())),
                m -> m.entrySet().stream().map(e -> new DataSet(e.getKey(), e.getValue())).collect(toList())));
}

Stream API with map merging: Instead of flattening the original data structures, you can also create a Map for each MultiDataPoint, and then merge all maps into a single map with a reduce operation. The code is a bit simpler than the above solution:

Collection<DataSet> convert(List<MultiDataPoint> multiDataPoints) {
    return multiDataPoints.stream()
        .map(mdp -> mdp.keyToData.entrySet().stream()
            .collect(toMap(e -> e.getKey(), e -> asList(new DataPoint(mdp.timestamp, e.getValue())))))
        .reduce(new HashMap<>(), mapMerger())
        .entrySet().stream()
        .map(e -> new DataSet(e.getKey(), e.getValue()))
        .collect(toList());
}

You can find an implementation of the map merger within the Collectors class. Unfortunately, it is a bit tricky to access it from the outside. Following is an alternative implementation of the map merger:

<K, V> BinaryOperator<Map<K, List<V>>> mapMerger() {
    return (lhs, rhs) -> {
        Map<K, List<V>> result = new HashMap<>();
        lhs.forEach((key, value) -> result.computeIfAbsent(key, k -> new ArrayList<>()).addAll(value));
        rhs.forEach((key, value) -> result.computeIfAbsent(key, k -> new ArrayList<>()).addAll(value));
        return result;
    };
}

Java 8 Lambda filter by Lists

Predicate<Client> hasSameNameAsOneUser = 
    c -> users.stream().anyMatch(u -> u.getName().equals(c.getName()));

return clients.stream()
              .filter(hasSameNameAsOneUser)
              .collect(Collectors.toList());

But this is quite inefficient, because it's O(m * n). You'd better create a Set of acceptable names:

Set<String> acceptableNames = 
    users.stream()
         .map(User::getName)
         .collect(Collectors.toSet());

return clients.stream()
              .filter(c -> acceptableNames.contains(c.getName()))
              .collect(Collectors.toList());

Also note that it's not strictly equivalent to the code you have (if it compiled), which adds the same client twice to the list if several users have the same name as the client.

Why would you use Expression<Func<T>> rather than Func<T>?

I don't see any answers yet that mention performance. Passing Func<>s into Where() or Count() is bad. Real bad. If you use a Func<> then it calls the IEnumerable LINQ stuff instead of IQueryable, which means that whole tables get pulled in and then filtered. Expression<Func<>> is significantly faster, especially if you are querying a database that lives another server.

python max function using 'key' and lambda expression

lambda is an anonymous function, it is equivalent to:

def func(p):
   return p.totalScore     

Now max becomes:

max(players, key=func)

But as def statements are compound statements they can't be used where an expression is required, that's why sometimes lambda's are used.

Note that lambda is equivalent to what you'd put in a return statement of a def. Thus, you can't use statements inside a lambda, only expressions are allowed.


What does max do?

max(a, b, c, ...[, key=func]) -> value

With a single iterable argument, return its largest item. With two or more arguments, return the largest argument.

So, it simply returns the object that is the largest.


How does key work?

By default in Python 2 key compares items based on a set of rules based on the type of the objects (for example a string is always greater than an integer).

To modify the object before comparison, or to compare based on a particular attribute/index, you've to use the key argument.

Example 1:

A simple example, suppose you have a list of numbers in string form, but you want to compare those items by their integer value.

>>> lis = ['1', '100', '111', '2']

Here max compares the items using their original values (strings are compared lexicographically so you'd get '2' as output) :

>>> max(lis)
'2'

To compare the items by their integer value use key with a simple lambda:

>>> max(lis, key=lambda x:int(x))  # compare `int` version of each item
'111'

Example 2: Applying max to a list of tuples.

>>> lis = [(1,'a'), (3,'c'), (4,'e'), (-1,'z')]

By default max will compare the items by the first index. If the first index is the same then it'll compare the second index. As in my example, all items have a unique first index, so you'd get this as the answer:

>>> max(lis)
(4, 'e')

But, what if you wanted to compare each item by the value at index 1? Simple: use lambda:

>>> max(lis, key = lambda x: x[1])
(-1, 'z')

Comparing items in an iterable that contains objects of different type:

List with mixed items:

lis = ['1','100','111','2', 2, 2.57]

In Python 2 it is possible to compare items of two different types:

>>> max(lis)  # works in Python 2
'2'
>>> max(lis, key=lambda x: int(x))  # compare integer version of each item
'111'

But in Python 3 you can't do that any more:

>>> lis = ['1', '100', '111', '2', 2, 2.57]
>>> max(lis)
Traceback (most recent call last):
  File "<ipython-input-2-0ce0a02693e4>", line 1, in <module>
    max(lis)
TypeError: unorderable types: int() > str()

But this works, as we are comparing integer version of each object:

>>> max(lis, key=lambda x: int(x))  # or simply `max(lis, key=int)`
'111'

Is there a way to perform "if" in python's lambda

Probably the worst python line I've written so far:

f = lambda x: sys.stdout.write(["2\n",][2*(x==2)-2])

If x == 2 you print,

if x != 2 you raise.

Passing capturing lambda as function pointer

As it was mentioned by the others you can substitute Lambda function instead of function pointer. I am using this method in my C++ interface to F77 ODE solver RKSUITE.

//C interface to Fortran subroutine UT
extern "C"  void UT(void(*)(double*,double*,double*),double*,double*,double*,
double*,double*,double*,int*);

// C++ wrapper which calls extern "C" void UT routine
static  void   rk_ut(void(*)(double*,double*,double*),double*,double*,double*,
double*,double*,double*,int*);

//  Call of rk_ut with lambda passed instead of function pointer to derivative
//  routine
mathlib::RungeKuttaSolver::rk_ut([](double* T,double* Y,double* YP)->void{YP[0]=Y[1]; YP[1]= -Y[0];}, TWANT,T,Y,YP,YMAX,WORK,UFLAG);

Java 8 stream map to list of keys sorted by values

You have to sort with a custom comparator based on the value of the entry. Then select all the keys before collecting

countByType.entrySet()
           .stream()
           .sorted((e1, e2) -> e1.getValue().compareTo(e2.getValue())) // custom Comparator
           .map(e -> e.getKey())
           .collect(Collectors.toList());

Join/Where with LINQ and Lambda

I find that if you're familiar with SQL syntax, using the LINQ query syntax is much clearer, more natural, and makes it easier to spot errors:

var id = 1;
var query =
   from post in database.Posts
   join meta in database.Post_Metas on post.ID equals meta.Post_ID
   where post.ID == id
   select new { Post = post, Meta = meta };

If you're really stuck on using lambdas though, your syntax is quite a bit off. Here's the same query, using the LINQ extension methods:

var id = 1;
var query = database.Posts    // your starting point - table in the "from" statement
   .Join(database.Post_Metas, // the source table of the inner join
      post => post.ID,        // Select the primary key (the first part of the "on" clause in an sql "join" statement)
      meta => meta.Post_ID,   // Select the foreign key (the second part of the "on" clause)
      (post, meta) => new { Post = post, Meta = meta }) // selection
   .Where(postAndMeta => postAndMeta.Post.ID == id);    // where statement

convert a list of objects from one type to another using lambda expression

I believe something like this should work:

origList.Select(a => new TargetType() { SomeValue = a.SomeValue});

Filter values only if not null using lambda in Java8

The proposed answers are great. Just would like to suggest an improvement to handle the case of null list using Optional.ofNullable, new feature in Java 8:

 List<String> carsFiltered = Optional.ofNullable(cars)
                .orElseGet(Collections::emptyList)
                .stream()
                .filter(Objects::nonNull)
                .collect(Collectors.toList());

So, the full answer will be:

 List<String> carsFiltered = Optional.ofNullable(cars)
                .orElseGet(Collections::emptyList)
                .stream()
                .filter(Objects::nonNull) //filtering car object that are null
                .map(Car::getName) //now it's a stream of Strings
                .filter(Objects::nonNull) //filtering null in Strings
                .filter(name -> name.startsWith("M"))
                .collect(Collectors.toList()); //back to List of Strings

Java 8, Streams to find the duplicate elements

My StreamEx library which enhances the Java 8 streams provides a special operation distinct(atLeast) which can retain only elements appearing at least the specified number of times. So your problem can be solved like this:

List<Integer> repeatingNumbers = StreamEx.of(numbers).distinct(2).toList();

Internally it's similar to @Dave solution, it counts objects, to support other wanted quantities and it's parallel-friendly (it uses ConcurrentHashMap for parallelized stream, but HashMap for sequential). For big amounts of data you can get a speed-up using .parallel().distinct(2).

Modifying local variable from inside lambda

An alternative to AtomicInteger is to use an array (or any other object able to store a value):

final int ordinal[] = new int[] { 0 };
list.forEach ( s -> s.setOrdinal ( ordinal[ 0 ]++ ) );

But see the Stuart's answer: there might be a better way to deal with your case.

Filter Java Stream to 1 and only 1 element

Using a Collector:

public static <T> Collector<T, ?, Optional<T>> toSingleton() {
    return Collectors.collectingAndThen(
            Collectors.toList(),
            list -> list.size() == 1 ? Optional.of(list.get(0)) : Optional.empty()
    );
}

Usage:

Optional<User> result = users.stream()
        .filter((user) -> user.getId() < 0)
        .collect(toSingleton());

We return an Optional, since we usually can't assume the Collection to contain exactly one element. If you already know this is the case, call:

User user = result.orElseThrow();

This puts the burden of handeling the error on the caller - as it should.

Order a List (C#) by many fields?

Use ThenBy:

var orderedCustomers = Customer.OrderBy(c => c.LastName).ThenBy(c => c.FirstName)

See MSDN: http://msdn.microsoft.com/en-us/library/bb549422.aspx

How to sort with a lambda?

To much code, you can use it like this:

#include<array>
#include<functional>

int main()
{
    std::array<int, 10> vec = { 1,2,3,4,5,6,7,8,9 };

    std::sort(std::begin(vec), 
              std::end(vec), 
              [](int a, int b) {return a > b; });

    for (auto item : vec)
      std::cout << item << " ";

    return 0;
}

Replace "vec" with your class and that's it.

Multiple Where clauses in Lambda expressions

The lambda you pass to Where can include any normal C# code, for example the && operator:

.Where(l => l.Title != string.Empty && l.InternalName != string.Empty)

How to properly apply a lambda function into a pandas data frame column

You need to add else in your lambda function. Because you are telling what to do in case your condition(here x < 90) is met, but you are not telling what to do in case the condition is not met.

sample['PR'] = sample['PR'].apply(lambda x: 'NaN' if x < 90 else x) 

Difference between final and effectively final

'Effectively final' is a variable which would not give compiler error if it were to be appended by 'final'

From a article by 'Brian Goetz',

Informally, a local variable is effectively final if its initial value is never changed -- in other words, declaring it final would not cause a compilation failure.

lambda-state-final- Brian Goetz

Variable used in lambda expression should be final or effectively final

Java 8 has a new concept called “Effectively final” variable. It means that a non-final local variable whose value never changes after initialization is called “Effectively Final”.

This concept was introduced because prior to Java 8, we could not use a non-final local variable in an anonymous class. If you wanna have access to a local variable in anonymous class, you have to make it final.

When lambda was introduced, this restriction was eased. Hence to the need to make local variable final if it’s not changed once it is initialized as lambda in itself is nothing but an anonymous class.

Java 8 realized the pain of declaring local variable final every time a developer used lambda, introduced this concept, and made it unnecessary to make local variables final. So if you see the rule for anonymous classes has not changed, it’s just you don’t have to write the final keyword every time when using lambdas.

I found a good explanation here

Retrieving Property name from lambda expression

static void Main(string[] args)
{
    var prop = GetPropertyInfo<MyDto>(_ => _.MyProperty);

    MyDto dto = new MyDto();
    dto.MyProperty = 666;

    var value = prop.GetValue(dto);
    // value == 666
}

class MyDto
{
    public int MyProperty { get; set; }
}

public static PropertyInfo GetPropertyInfo<TSource>(Expression<Func<TSource, object>> propertyLambda)
{
    Type type = typeof(TSource);

    var member = propertyLambda.Body as MemberExpression;
    if (member == null)
    {
        var unary = propertyLambda.Body as UnaryExpression;
        if (unary != null)
        {
            member = unary.Operand as MemberExpression;
        }
    }
    if (member == null)
    {
        throw new ArgumentException(string.Format("Expression '{0}' refers to a method, not a property.",
            propertyLambda.ToString()));
    }

    var propInfo = member.Member as PropertyInfo;
    if (propInfo == null)
    {
        throw new ArgumentException(string.Format("Expression '{0}' refers to a field, not a property.",
            propertyLambda.ToString()));
    }

    if (type != propInfo.ReflectedType && !type.IsSubclassOf(propInfo.ReflectedType))
    {
        throw new ArgumentException(string.Format("Expression '{0}' refers to a property that is not from type {1}.",
            propertyLambda.ToString(), type));
    }

    return propInfo;
}

C# Lambda expressions: Why should I use them?

It saves having to have methods that are only used once in a specific place from being defined far away from the place they are used. Good uses are as comparators for generic algorithms such as sorting, where you can then define a custom sort function where you are invoking the sort rather than further away forcing you to look elsewhere to see what you are sorting on.

And it's not really an innovation. LISP has had lambda functions for about 30 years or more.

Combining two expressions (Expression<Func<T, bool>>)

I combined some beautiful answers here to make it possible to easily support more Expression operators.

This is based on the answer of @Dejan but now it's quite easy to add the OR as well. I chose not to make the Combine function public, but you could do that to be even more flexible.

public static class ExpressionExtensions
{
    public static Expression<Func<T, bool>> AndAlso<T>(this Expression<Func<T, bool>> leftExpression,
        Expression<Func<T, bool>> rightExpression) =>
        Combine(leftExpression, rightExpression, Expression.AndAlso);

    public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> leftExpression,
        Expression<Func<T, bool>> rightExpression) =>
        Combine(leftExpression, rightExpression, Expression.Or);

    public static Expression<Func<T, bool>> Combine<T>(Expression<Func<T, bool>> leftExpression, Expression<Func<T, bool>> rightExpression, Func<Expression, Expression, BinaryExpression> combineOperator)
    {
        var leftParameter = leftExpression.Parameters[0];
        var rightParameter = rightExpression.Parameters[0];

        var visitor = new ReplaceParameterVisitor(rightParameter, leftParameter);

        var leftBody = leftExpression.Body;
        var rightBody = visitor.Visit(rightExpression.Body);

        return Expression.Lambda<Func<T, bool>>(combineOperator(leftBody, rightBody), leftParameter);
    }

    private class ReplaceParameterVisitor : ExpressionVisitor
    {
        private readonly ParameterExpression _oldParameter;
        private readonly ParameterExpression _newParameter;

        public ReplaceParameterVisitor(ParameterExpression oldParameter, ParameterExpression newParameter)
        {
            _oldParameter = oldParameter;
            _newParameter = newParameter;
        }

        protected override Expression VisitParameter(ParameterExpression node)
        {
            return ReferenceEquals(node, _oldParameter) ? _newParameter : base.VisitParameter(node);
        }
    }
}

Usage is not changed and still like this:

Expression<Func<Result, bool>> noFilterExpression = item => filters == null;

Expression<Func<Result, bool>> laptopFilterExpression = item => item.x == ...
Expression<Func<Result, bool>> dateFilterExpression = item => item.y == ...

var combinedFilterExpression = noFilterExpression.Or(laptopFilterExpression.AndAlso(dateFilterExpression));
    
efQuery.Where(combinedFilterExpression);

(This is an example based on my actual code, but read is as pseudo-code)

List<T> OrderBy Alphabetical Order

you can use linq :) using :

System.linq;
var newList = people.OrderBy(x=>x.Name).ToList();

Java 8 Streams: multiple filters vs. complex condition

The code that has to be executed for both alternatives is so similar that you can’t predict a result reliably. The underlying object structure might differ but that’s no challenge to the hotspot optimizer. So it depends on other surrounding conditions which will yield to a faster execution, if there is any difference.

Combining two filter instances creates more objects and hence more delegating code but this can change if you use method references rather than lambda expressions, e.g. replace filter(x -> x.isCool()) by filter(ItemType::isCool). That way you have eliminated the synthetic delegating method created for your lambda expression. So combining two filters using two method references might create the same or lesser delegation code than a single filter invocation using a lambda expression with &&.

But, as said, this kind of overhead will be eliminated by the HotSpot optimizer and is negligible.

In theory, two filters could be easier parallelized than a single filter but that’s only relevant for rather computational intense tasks¹.

So there is no simple answer.

The bottom line is, don’t think about such performance differences below the odor detection threshold. Use what is more readable.


¹…and would require an implementation doing parallel processing of subsequent stages, a road currently not taken by the standard Stream implementation

FirstOrDefault returns NullReferenceException if no match is found

To add to the solutions, here is a LINQ statement that might help

Utilities.DIMENSION_MemTbl.Where(a => a.DIMENSION_ID == format.ContentBrief.DimensionID).Select(a=>a.DIMENSION1).DefaultIfEmpty("").FirstOrDefault();

The result will be an empty string if the result of the query is a null..

LINQ where clause with lambda expression having OR clauses and null values returning incomplete results

Your second delegate is not a rewrite of the first in anonymous delegate (rather than lambda) format. Look at your conditions.

First:

x.ID == packageId || x.Parent.ID == packageId || x.Parent.Parent.ID == packageId

Second:

(x.ID == packageId) || (x.Parent != null && x.Parent.ID == packageId) || 
(x.Parent != null && x.Parent.Parent != null && x.Parent.Parent.ID == packageId)

The call to the lambda would throw an exception for any x where the ID doesn't match and either the parent is null or doesn't match and the grandparent is null. Copy the null checks into the lambda and it should work correctly.

Edit after Comment to Question

If your original object is not a List<T>, then we have no way of knowing what the return type of FindAll() is, and whether or not this implements the IQueryable interface. If it does, then that likely explains the discrepancy. Because lambdas can be converted at compile time into an Expression<Func<T>> but anonymous delegates cannot, then you may be using the implementation of IQueryable when using the lambda version but LINQ-to-Objects when using the anonymous delegate version.

This would also explain why your lambda is not causing a NullReferenceException. If you were to pass that lambda expression to something that implements IEnumerable<T> but not IQueryable<T>, runtime evaluation of the lambda (which is no different from other methods, anonymous or not) would throw a NullReferenceException the first time it encountered an object where ID was not equal to the target and the parent or grandparent was null.

Added 3/16/2011 8:29AM EDT

Consider the following simple example:

IQueryable<MyObject> source = ...; // some object that implements IQueryable<MyObject>

var anonymousMethod =  source.Where(delegate(MyObject o) { return o.Name == "Adam"; });    
var expressionLambda = source.Where(o => o.Name == "Adam");

These two methods produce entirely different results.

The first query is the simple version. The anonymous method results in a delegate that's then passed to the IEnumerable<MyObject>.Where extension method, where the entire contents of source will be checked (manually in memory using ordinary compiled code) against your delegate. In other words, if you're familiar with iterator blocks in C#, it's something like doing this:

public IEnumerable<MyObject> MyWhere(IEnumerable<MyObject> dataSource, Func<MyObject, bool> predicate)
{
    foreach(MyObject item in dataSource)
    {
        if(predicate(item)) yield return item;
    }
}

The salient point here is that you're actually performing your filtering in memory on the client side. For example, if your source were some SQL ORM, there would be no WHERE clause in the query; the entire result set would be brought back to the client and filtered there.

The second query, which uses a lambda expression, is converted to an Expression<Func<MyObject, bool>> and uses the IQueryable<MyObject>.Where() extension method. This results in an object that is also typed as IQueryable<MyObject>. All of this works by then passing the expression to the underlying provider. This is why you aren't getting a NullReferenceException. It's entirely up to the query provider how to translate the expression (which, rather than being an actual compiled function that it can just call, is a representation of the logic of the expression using objects) into something it can use.

An easy way to see the distinction (or, at least, that there is) a distinction, would be to put a call to AsEnumerable() before your call to Where in the lambda version. This will force your code to use LINQ-to-Objects (meaning it operates on IEnumerable<T> like the anonymous delegate version, not IQueryable<T> like the lambda version currently does), and you'll get the exceptions as expected.

TL;DR Version

The long and the short of it is that your lambda expression is being translated into some kind of query against your data source, whereas the anonymous method version is evaluating the entire data source in memory. Whatever is doing the translating of your lambda into a query is not representing the logic that you're expecting, which is why it isn't producing the results you're expecting.

Can lambda functions be templated?

In C++20 this is possible using the following syntax:

auto lambda = []<typename T>(T t){
    // do something
};

C# Pass Lambda Expression as Method Parameter

Use a Func<T1, T2, TResult> delegate as the parameter type and pass it in to your Query:

public List<IJob> getJobs(Func<FullTimeJob, Student, FullTimeJob> lambda)
{
  using (SqlConnection connection = new SqlConnection(getConnectionString())) {
    connection.Open();
    return connection.Query<FullTimeJob, Student, FullTimeJob>(sql, 
        lambda,
        splitOn: "user_id",
        param: parameters).ToList<IJob>();   
  }  
}

You would call it:

getJobs((job, student) => {         
        job.Student = student;
        job.StudentId = student.Id;
        return job;
        });

Or assign the lambda to a variable and pass it in.

How to perform Join between multiple tables in LINQ lambda

 public ActionResult Index()
    {
        List<CustomerOrder_Result> obj = new List<CustomerOrder_Result>();

       var  orderlist = (from a in db.OrderMasters
                         join b in db.Customers on a.CustomerId equals b.Id
                         join c in db.CustomerAddresses on b.Id equals c.CustomerId
                         where a.Status == "Pending"
                         select new
                         {
                             Customername = b.Customername,
                             Phone = b.Phone,
                             OrderId = a.OrderId,
                             OrderDate = a.OrderDate,
                             NoOfItems = a.NoOfItems,
                             Order_amt = a.Order_amt,
                             dis_amt = a.Dis_amt,
                             net_amt = a.Net_amt,
                             status=a.Status,  
                             address = c.address,
                             City = c.City,
                             State = c.State,
                             Pin = c.Pin

                         }) ;
       foreach (var item in orderlist)
       {

           CustomerOrder_Result clr = new CustomerOrder_Result();
           clr.Customername=item.Customername;
           clr.Phone = item.Phone;
           clr.OrderId = item.OrderId;
           clr.OrderDate = item.OrderDate;
           clr.NoOfItems = item.NoOfItems;
           clr.Order_amt = item.Order_amt;
           clr.net_amt = item.net_amt;
           clr.address = item.address;
           clr.City = item.City;
           clr.State = item.State;
           clr.Pin = item.Pin;
           clr.status = item.status;

           obj.Add(clr);



       }

Conditional statement in a one line lambda function in python?

Use the exp1 if cond else exp2 syntax.

rate = lambda T: 200*exp(-T) if T>200 else 400*exp(-T)

Note you don't use return in lambda expressions.

Java 8: Lambda-Streams, Filter by Method with Exception

You can potentially roll your own Stream variant by wrapping your lambda to throw an unchecked exception and then later unwrapping that unchecked exception on terminal operations:

@FunctionalInterface
public interface ThrowingPredicate<T, X extends Throwable> {
    public boolean test(T t) throws X;
}

@FunctionalInterface
public interface ThrowingFunction<T, R, X extends Throwable> {
    public R apply(T t) throws X;
}

@FunctionalInterface
public interface ThrowingSupplier<R, X extends Throwable> {
    public R get() throws X;
}

public interface ThrowingStream<T, X extends Throwable> {
    public ThrowingStream<T, X> filter(
            ThrowingPredicate<? super T, ? extends X> predicate);

    public <R> ThrowingStream<T, R> map(
            ThrowingFunction<? super T, ? extends R, ? extends X> mapper);

    public <A, R> R collect(Collector<? super T, A, R> collector) throws X;

    // etc
}

class StreamAdapter<T, X extends Throwable> implements ThrowingStream<T, X> {
    private static class AdapterException extends RuntimeException {
        public AdapterException(Throwable cause) {
            super(cause);
        }
    }

    private final Stream<T> delegate;
    private final Class<X> x;

    StreamAdapter(Stream<T> delegate, Class<X> x) {
        this.delegate = delegate;
        this.x = x;
    }

    private <R> R maskException(ThrowingSupplier<R, X> method) {
        try {
            return method.get();
        } catch (Throwable t) {
            if (x.isInstance(t)) {
                throw new AdapterException(t);
            } else {
                throw t;
            }
        }
    }

    @Override
    public ThrowingStream<T, X> filter(ThrowingPredicate<T, X> predicate) {
        return new StreamAdapter<>(
                delegate.filter(t -> maskException(() -> predicate.test(t))), x);
    }

    @Override
    public <R> ThrowingStream<R, X> map(ThrowingFunction<T, R, X> mapper) {
        return new StreamAdapter<>(
                delegate.map(t -> maskException(() -> mapper.apply(t))), x);
    }

    private <R> R unmaskException(Supplier<R> method) throws X {
        try {
            return method.get();
        } catch (AdapterException e) {
            throw x.cast(e.getCause());
        }
    }

    @Override
    public <A, R> R collect(Collector<T, A, R> collector) throws X {
        return unmaskException(() -> delegate.collect(collector));
    }
}

Then you could use this the same exact way as a Stream:

Stream<Account> s = accounts.values().stream();
ThrowingStream<Account, IOException> ts = new StreamAdapter<>(s, IOException.class);
return ts.filter(Account::isActive).map(Account::getNumber).collect(toSet());

This solution would require quite a bit of boilerplate, so I suggest you take a look at the library I already made which does exactly what I have described here for the entire Stream class (and more!).

Finding the average of a list

sum(l) / float(len(l)) is the right answer, but just for completeness you can compute an average with a single reduce:

>>> reduce(lambda x, y: x + y / float(len(l)), l, 0)
20.111111111111114

Note that this can result in a slight rounding error:

>>> sum(l) / float(len(l))
20.111111111111111

Java 8 lambdas, Function.identity() or t->t

As of the current JRE implementation, Function.identity() will always return the same instance while each occurrence of identifier -> identifier will not only create its own instance but even have a distinct implementation class. For more details, see here.

The reason is that the compiler generates a synthetic method holding the trivial body of that lambda expression (in the case of x->x, equivalent to return identifier;) and tell the runtime to create an implementation of the functional interface calling this method. So the runtime sees only different target methods and the current implementation does not analyze the methods to find out whether certain methods are equivalent.

So using Function.identity() instead of x -> x might save some memory but that shouldn’t drive your decision if you really think that x -> x is more readable than Function.identity().

You may also consider that when compiling with debug information enabled, the synthetic method will have a line debug attribute pointing to the source code line(s) holding the lambda expression, therefore you have a chance of finding the source of a particular Function instance while debugging. In contrast, when encountering the instance returned by Function.identity() during debugging an operation, you won’t know who has called that method and passed the instance to the operation.

What are functional interfaces used for in Java 8?

@FunctionalInterface annotation is useful for compilation time checking of your code. You cannot have more than one method besides static, default and abstract methods that override methods in Object in your @FunctionalInterface or any other interface used as a functional interface.

But you can use lambdas without this annotation as well as you can override methods without @Override annotation.

From docs

a functional interface has exactly one abstract method. Since default methods have an implementation, they are not abstract. If an interface declares an abstract method overriding one of the public methods of java.lang.Object, that also does not count toward the interface's abstract method count since any implementation of the interface will have an implementation from java.lang.Object or elsewhere

This can be used in lambda expression:

public interface Foo {
  public void doSomething();
}

This cannot be used in lambda expression:

public interface Foo {
  public void doSomething();
  public void doSomethingElse();
}

But this will give compilation error:

@FunctionalInterface
public interface Foo {
  public void doSomething();
  public void doSomethingElse();
}

Invalid '@FunctionalInterface' annotation; Foo is not a functional interface

Java 8 lambda Void argument

Use Supplier if it takes nothing, but returns something.

Use Consumer if it takes something, but returns nothing.

Use Callable if it returns a result and might throw (most akin to Thunk in general CS terms).

Use Runnable if it does neither and cannot throw.

Break or return from Java 8 stream forEach?

int valueToMatch = 7;
Stream.of(1,2,3,4,5,6,7,8).anyMatch(val->{
   boolean isMatch = val == valueToMatch;
   if(isMatch) {
      /*Do whatever you want...*/
       System.out.println(val);
   }
   return isMatch;
});

It will do only operation where it find match, and after find match it stop it's iteration.

Python one-line "for" expression

The keyword you're looking for is list comprehensions:

>>> x = [1, 2, 3, 4, 5]
>>> y = [2*a for a in x if a % 2 == 1]
>>> print(y)
[2, 6, 10]

Task.Run with Parameter(s)?

Just use Task.Run

var task = Task.Run(() =>
{
    //this will already share scope with rawData, no need to use a placeholder
});

Or, if you would like to use it in a method and await the task later

public Task<T> SomethingAsync<T>()
{
    var task = Task.Run(() =>
    {
        //presumably do something which takes a few ms here
        //this will share scope with any passed parameters in the method
        return default(T);
    });

    return task;
}

Java 8 Lambda function that throws exception?

You can.

Extending @marcg 's UtilException and adding generic <E extends Exception> where necessary: this way, the compiler will force you again to add throw clauses and everything's as if you could throw checked exceptions natively on java 8's streams.

public final class LambdaExceptionUtil {

    @FunctionalInterface
    public interface Function_WithExceptions<T, R, E extends Exception> {
        R apply(T t) throws E;
    }

    /**
     * .map(rethrowFunction(name -> Class.forName(name))) or .map(rethrowFunction(Class::forName))
     */
    public static <T, R, E extends Exception> Function<T, R> rethrowFunction(Function_WithExceptions<T, R, E> function) throws E  {
        return t -> {
            try {
                return function.apply(t);
            } catch (Exception exception) {
                throwActualException(exception);
                return null;
            }
        };
    }

    @SuppressWarnings("unchecked")
    private static <E extends Exception> void throwActualException(Exception exception) throws E {
        throw (E) exception;
    }

}

public class LambdaExceptionUtilTest {

    @Test
    public void testFunction() throws MyTestException {
        List<Integer> sizes = Stream.of("ciao", "hello").<Integer>map(rethrowFunction(s -> transform(s))).collect(toList());
        assertEquals(2, sizes.size());
        assertEquals(4, sizes.get(0).intValue());
        assertEquals(5, sizes.get(1).intValue());
    }

    private Integer transform(String value) throws MyTestException {
        if(value==null) {
            throw new MyTestException();
        }
        return value.length();
    }

    private static class MyTestException extends Exception { }
}

Change some value inside the List<T>

You could use ForEach, but you have to convert the IEnumerable<T> to a List<T> first.

list.Where(w => w.Name == "height").ToList().ForEach(s => s.Value = 30);

Retrieving a List from a java.util.stream.Stream in Java 8

What you are doing may be the simplest way, provided your stream stays sequential—otherwise you will have to put a call to sequential() before forEach.

[later edit: the reason the call to sequential() is necessary is that the code as it stands (forEach(targetLongList::add)) would be racy if the stream was parallel. Even then, it will not achieve the effect intended, as forEach is explicitly nondeterministic—even in a sequential stream the order of element processing is not guaranteed. You would have to use forEachOrdered to ensure correct ordering. The intention of the Stream API designers is that you will use collector in this situation, as below.]

An alternative is

targetLongList = sourceLongList.stream()
    .filter(l -> l > 100)
    .collect(Collectors.toList());

Syntax behind sorted(key=lambda: ...)

Since the usage of lambda was asked in the context of sorted(), take a look at this as well https://wiki.python.org/moin/HowTo/Sorting/#Key_Functions

What is the difference between a 'closure' and a 'lambda'?

It's as simple as this: lambda is a language construct, i.e. simply syntax for anonymous functions; a closure is a technique to implement it -- or any first-class functions, for that matter, named or anonymous.

More precisely, a closure is how a first-class function is represented at runtime, as a pair of its "code" and an environment "closing" over all the non-local variables used in that code. This way, those variables are still accessible even when the outer scopes where they originate have already been exited.

Unfortunately, there are many languages out there that do not support functions as first-class values, or only support them in crippled form. So people often use the term "closure" to distinguish "the real thing".

Lambda expression to convert array/List of String to array/List of Integers

For List :

List<Integer> intList 
 = stringList.stream().map(Integer::valueOf).collect(Collectors.toList());

For Array :

int[] intArray = Arrays.stream(stringArray).mapToInt(Integer::valueOf).toArray();

Using lambda expressions for event handlers

EventHandler handler = (s, e) => MessageBox.Show("Woho");

button.Click += handler;
button.Click -= handler;

C# Syntax - Example of a Lambda Expression - ForEach() over Generic List

Want to put out there that there is not much to worry about if someone provides an answer as an extension method because an extension method is just a cool way to call an instance method. I understand that you want the answer without using an extension method. Regardless if the method is defined as static, instance or extension - the result is the same.

The code below uses the code from the accepted answer to define an extension method and an instance method and creates a unit test to show the output is the same.

public static class Extensions
{
    public static void Each<T>(this IEnumerable<T> items, Action<T> action)
    {
        foreach (var item in items)
        {
            action(item);
        }
    }
}

[TestFixture]
public class ForEachTests
{
    public void Each<T>(IEnumerable<T> items, Action<T> action)
    {
        foreach (var item in items)
        {
            action(item);
        }
    }

    private string _extensionOutput;

    private void SaveExtensionOutput(string value)
    {
        _extensionOutput += value;
    }

    private string _instanceOutput;

    private void SaveInstanceOutput(string value)
    {
        _instanceOutput += value;
    }

    [Test]
    public void Test1()
    {
        string[] teams = new string[] {"cowboys", "falcons", "browns", "chargers", "rams", "seahawks", "lions", "heat", "blackhawks", "penguins", "pirates"};

        Each(teams, SaveInstanceOutput);

        teams.Each(SaveExtensionOutput);

        Assert.AreEqual(_extensionOutput, _instanceOutput);
    }
}

Quite literally, the only thing you need to do to convert an extension method to an instance method is remove the static modifier and the first parameter of the method.

This method

public static void Each<T>(this IEnumerable<T> items, Action<T> action)
{
    foreach (var item in items)
    {
        action(item);
    }
 }

becomes

public void Each<T>(Action<T> action)
{
    foreach (var item in items)
    {
        action(item);
    }
 }

Java 8 Filter Array Using Lambda

Yes, you can do this by creating a DoubleStream from the array, filtering out the negatives, and converting the stream back to an array. Here is an example:

double[] d = {8, 7, -6, 5, -4};
d = Arrays.stream(d).filter(x -> x > 0).toArray();
//d => [8, 7, 5]

If you want to filter a reference array that is not an Object[] you will need to use the toArray method which takes an IntFunction to get an array of the original type as the result:

String[] a = { "s", "", "1", "", "" };
a = Arrays.stream(a).filter(s -> !s.isEmpty()).toArray(String[]::new);

Android, ListView IllegalStateException: "The content of the adapter has changed but ListView did not receive a notification"

I had the same sittuation , I had many buttongroup insite my item on listview and I was changing some boolean values inside my item like holder.rbVar.setOnclik...

my problem occured because I was calling a method inside getView(); and was saving an object inside sharepreference, so I had same error above

How I solved it; I removed my method inside getView() to notifyDataSetInvalidated() and problem gone

   @Override
    public void notifyDataSetChanged() {
        saveCurrentTalebeOnShare(currentTalebe);
        super.notifyDataSetChanged();
    }

jQuery show/hide options from one select drop down, when option on other select dropdown is slected

// find the first select and bind a click handler
$('#column_select').bind('click', function(){
    // retrieve the selected value
    var value = $(this).val(),
        // build a regular expression that does a head-match
        expression = new RegExp('^' + value),
        // find the second select
        $select = $('#layout_select);

    // hide all children (<option>s) of the second select,
    // check each element's value agains the regular expression built from the first select's value
    // show elements that match the expression
    $select.children().hide().filter(function(){
      return !!$(this).val().match(expression);
    }).show();
});

(this is far from perfect, but should get you there…)

How to do parallel programming in Python?

You can use joblib library to do parallel computation and multiprocessing.

from joblib import Parallel, delayed

You can simply create a function foo which you want to be run in parallel and based on the following piece of code implement parallel processing:

output = Parallel(n_jobs=num_cores)(delayed(foo)(i) for i in input)

Where num_cores can be obtained from multiprocessing library as followed:

import multiprocessing

num_cores = multiprocessing.cpu_count()

If you have a function with more than one input argument, and you just want to iterate over one of the arguments by a list, you can use the the partial function from functools library as follow:

from joblib import Parallel, delayed
import multiprocessing
from functools import partial
def foo(arg1, arg2, arg3, arg4):
    '''
    body of the function
    '''
    return output
input = [11,32,44,55,23,0,100,...] # arbitrary list
num_cores = multiprocessing.cpu_count()
foo_ = partial(foo, arg2=arg2, arg3=arg3, arg4=arg4)
# arg1 is being fetched from input list
output = Parallel(n_jobs=num_cores)(delayed(foo_)(i) for i in input)

You can find a complete explanation of the python and R multiprocessing with couple of examples here.

Reading json files in C++

  1. Yes you can create a nested data structure people which can be indexed by Anna and Ben. However, you can't index it directly by age and profession (I will get to this part in the code).

  2. The data type of people is of type Json::Value (which is defined in jsoncpp). You are right, it is similar to the nested map, but Value is a data structure which is defined such that multiple types can be stored and accessed. It is similar to a map with a string as the key and Json::Value as the value. It could also be a map between an unsigned int as key and Json::Value as the value (In case of json arrays).

Here's the code:

#include <json/value.h>
#include <fstream>

std::ifstream people_file("people.json", std::ifstream::binary);
people_file >> people;

cout<<people; //This will print the entire json object.

//The following lines will let you access the indexed objects.
cout<<people["Anna"]; //Prints the value for "Anna"
cout<<people["ben"]; //Prints the value for "Ben"
cout<<people["Anna"]["profession"]; //Prints the value corresponding to "profession" in the json for "Anna"

cout<<people["profession"]; //NULL! There is no element with key "profession". Hence a new empty element will be created.

As you can see, you can index the json object only based on the hierarchy of the input data.

Moment.js with Vuejs

// plugins/moment.js

import moment from 'moment';

moment.locale('ru');

export default function install (Vue) {
  Object.defineProperties(Vue.prototype, {
    $moment: {
      get () {
        return moment;
      }
    }
  })
}

// main.js

import moment from './plugins/moment.js';
Vue.use(moment);

// use this.$moment in your components

JWT refresh token flow

Assuming that this is about OAuth 2.0 since it is about JWTs and refresh tokens...:

  1. just like an access token, in principle a refresh token can be anything including all of the options you describe; a JWT could be used when the Authorization Server wants to be stateless or wants to enforce some sort of "proof-of-possession" semantics on to the client presenting it; note that a refresh token differs from an access token in that it is not presented to a Resource Server but only to the Authorization Server that issued it in the first place, so the self-contained validation optimization for JWTs-as-access-tokens does not hold for refresh tokens

  2. that depends on the security/access of the database; if the database can be accessed by other parties/servers/applications/users, then yes (but your mileage may vary with where and how you store the encryption key...)

  3. an Authorization Server may issue both access tokens and refresh tokens at the same time, depending on the grant that is used by the client to obtain them; the spec contains the details and options on each of the standardized grants

How do I do word Stemming or Lemmatization?

You could use the Morpha stemmer. UW has uploaded morpha stemmer to Maven central if you plan to use it from a Java application. There's a wrapper that makes it much easier to use. You just need to add it as a dependency and use the edu.washington.cs.knowitall.morpha.MorphaStemmer class. Instances are threadsafe (the original JFlex had class fields for local variables unnecessarily). Instantiate a class and run morpha and the word you want to stem.

new MorphaStemmer().morpha("climbed") // goes to "climb"

How can I display a pdf document into a Webview?

Download source code from here (Open pdf in webview android)

activity_main.xml

<RelativeLayout android:layout_width="match_parent"
                android:layout_height="match_parent"
                xmlns:android="http://schemas.android.com/apk/res/android">

    <WebView
        android:layout_width="match_parent"
        android:background="#ffffff"
        android:layout_height="match_parent"
        android:id="@+id/webview"></WebView>
</RelativeLayout>

MainActivity.java

package com.pdfwebview;

import android.app.ProgressDialog;
import android.graphics.Bitmap;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.webkit.WebView;
import android.webkit.WebViewClient;

public class MainActivity extends AppCompatActivity {

    WebView webview;
    ProgressDialog pDialog;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    init();
    listener();
    }

    private void init() {

        webview = (WebView) findViewById(R.id.webview);
        webview.getSettings().setJavaScriptEnabled(true);

        pDialog = new ProgressDialog(MainActivity.this);
        pDialog.setTitle("PDF");
        pDialog.setMessage("Loading...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
        webview.loadUrl("https://drive.google.com/file/d/0B534aayZ5j7Yc3RhcnRlcl9maWxl/view");

    }

    private void listener() {
        webview.setWebViewClient(new WebViewClient() {
            @Override
            public void onPageStarted(WebView view, String url, Bitmap favicon) {
                super.onPageStarted(view, url, favicon);
                pDialog.show();
            }

            @Override
            public void onPageFinished(WebView view, String url) {
                super.onPageFinished(view, url);
                pDialog.dismiss();
            }
        });
    }
}

Excel VBA, error 438 "object doesn't support this property or method

The Error is here

lastrow = wsPOR.Range("A" & Rows.Count).End(xlUp).Row + 1

wsPOR is a workbook and not a worksheet. If you are working with "Sheet1" of that workbook then try this

lastrow = wsPOR.Sheets("Sheet1").Range("A" & _
          wsPOR.Sheets("Sheet1").Rows.Count).End(xlUp).Row + 1

Similarly

wsPOR.Range("A2:G" & lastrow).Select

should be

wsPOR.Sheets("Sheet1").Range("A2:G" & lastrow).Select

Primitive type 'short' - casting in Java

Java always uses at least 32 bit values for calculations. This is due to the 32-bit architecture which was common 1995 when java was introduced. The register size in the CPU was 32 bit and the arithmetic logic unit accepted 2 numbers of the length of a cpu register. So the cpus were optimized for such values.

This is the reason why all datatypes which support arithmetic opperations and have less than 32-bits are converted to int (32 bit) as soon as you use them for calculations.

So to sum up it mainly was due to performance issues and is kept nowadays for compatibility.

Simplest PHP example for retrieving user_timeline with Twitter API version 1.1

Thank you Kris!

It worked for me without using parameters to the query, whenever I used more than one parameter it showed me the error: 32 Could not authenticate you.

The problem for me, was in the ampersand encoding. So in your code where it's the following line

$url .= "?".http_build_query($query);

I added the following line below:

$url=str_replace("&amp;","&",$url);

And it worked using two or more parameters like screen_name and count.

The whole code looks like this:

$token = 'YOUR TOKEN';
$token_secret = 'TOKEN SECRET';
$consumer_key = 'YOUR KEY';
$consumer_secret = 'KEY SECRET';

$host = 'api.twitter.com';
$method = 'GET';
$path = '/1.1/statuses/user_timeline.json'; // api call path

$query = array( // query parameters
    'screen_name' => 'twitterapi',
    'count' => '2'
);

$oauth = array(
    'oauth_consumer_key' => $consumer_key,
    'oauth_token' => $token,
    'oauth_nonce' => (string)mt_rand(), // a stronger nonce is recommended
    'oauth_timestamp' => time(),
    'oauth_signature_method' => 'HMAC-SHA1',
    'oauth_version' => '1.0'
);

$oauth = array_map("rawurlencode", $oauth); // must be encoded before sorting
$query = array_map("rawurlencode", $query);

$arr = array_merge($oauth, $query); // combine the values THEN sort

asort($arr); // secondary sort (value)
ksort($arr); // primary sort (key)

// http_build_query automatically encodes, but our parameters
// are already encoded, and must be by this point, so we undo
// the encoding step
$querystring = urldecode(http_build_query($arr, '', '&'));

$url = "https://$host$path";

// mash everything together for the text to hash
$base_string = $method."&".rawurlencode($url)."&".rawurlencode($querystring);

// same with the key
$key = rawurlencode($consumer_secret)."&".rawurlencode($token_secret);

// generate the hash
$signature = rawurlencode(base64_encode(hash_hmac('sha1', $base_string, $key, true)));

// this time we're using a normal GET query, and we're only encoding the query params
// (without the oauth params)
$url .= "?".http_build_query($query);
$url=str_replace("&amp;","&",$url); //Patch by @Frewuill

$oauth['oauth_signature'] = $signature; // don't want to abandon all that work!
ksort($oauth); // probably not necessary, but twitter's demo does it

// also not necessary, but twitter's demo does this too
function add_quotes($str) { return '"'.$str.'"'; }
$oauth = array_map("add_quotes", $oauth);

// this is the full value of the Authorization line
$auth = "OAuth " . urldecode(http_build_query($oauth, '', ', '));

// if you're doing post, you need to skip the GET building above
// and instead supply query parameters to CURLOPT_POSTFIELDS
$options = array( CURLOPT_HTTPHEADER => array("Authorization: $auth"),
                  //CURLOPT_POSTFIELDS => $postfields,
                  CURLOPT_HEADER => false,
                  CURLOPT_URL => $url,
                  CURLOPT_RETURNTRANSFER => true,
                  CURLOPT_SSL_VERIFYPEER => false);

// do our business
$feed = curl_init();
curl_setopt_array($feed, $options);
$json = curl_exec($feed);
curl_close($feed);

$twitter_data = json_decode($json);

Hope It helps somebody with the same problem I had.

How do I use Node.js Crypto to create a HMAC-SHA1 hash?

Documentation for crypto: http://nodejs.org/api/crypto.html

const crypto = require('crypto')

const text = 'I love cupcakes'
const key = 'abcdeg'

crypto.createHmac('sha1', key)
  .update(text)
  .digest('hex')

Get Value From Select Option in Angular 4

_x000D_
_x000D_
export class MyComponent implements OnInit {_x000D_
_x000D_
  items: any[] = [_x000D_
    { id: 1, name: 'one' },_x000D_
    { id: 2, name: 'two' },_x000D_
    { id: 3, name: 'three' },_x000D_
    { id: 4, name: 'four' },_x000D_
    { id: 5, name: 'five' },_x000D_
    { id: 6, name: 'six' }_x000D_
  ];_x000D_
  selected: number = 1;_x000D_
_x000D_
  constructor() {_x000D_
  }_x000D_
  _x000D_
  ngOnInit() {_x000D_
  }_x000D_
  _x000D_
  selectOption(id: number) {_x000D_
    //getted from event_x000D_
    console.log(id);_x000D_
    //getted from binding_x000D_
    console.log(this.selected)_x000D_
  }_x000D_
_x000D_
}
_x000D_
<div>_x000D_
  <select (change)="selectOption($event.target.value)"_x000D_
  [(ngModel)]="selected">_x000D_
  <option [value]="item.id" *ngFor="let item of items">{{item.name}}</option>_x000D_
   </select>_x000D_
</div> 
_x000D_
_x000D_
_x000D_

Groovy String to Date

The first argument to parse() is the expected format. You have to change that to Date.parse("E MMM dd H:m:s z yyyy", testDate) for it to work. (Note you don't need to create a new Date object, it's a static method)

If you don't know in advance what format, you'll have to find a special parsing library for that. In Ruby there's a library called Chronic, but I'm not aware of a Groovy equivalent. Edit: There is a Java port of the library called jChronic, you might want to check it out.

A quick and easy way to join array elements with a separator (the opposite of split) in Java

I prefer Google Collections over Apache StringUtils for this particular problem:

Joiner.on(separator).join(array)

Compared to StringUtils, the Joiner API has a fluent design and is a bit more flexible, e.g. null elements may be skipped or replaced by a placeholder. Also, Joiner has a feature for joining maps with a separator between key and value.

MySQL add days to a date

update tablename set coldate=DATE_ADD(coldate, INTERVAL 2 DAY)

paint() and repaint() in Java

It's not necessary to call repaint unless you need to render something specific onto a component. "Something specific" meaning anything that isn't provided internally by the windowing toolkit you're using.

Return content with IHttpActionResult for non-OK response

Above things are really helpful.

While creating web services, If you will take case of services consumer will greatly appreciated. I tried to maintain uniformity of the output. Also you can give remark or actual error message. The web service consumer can only check IsSuccess true or not else will sure there is problem, and act as per situation.

  public class Response
    {
        /// <summary>
        /// Gets or sets a value indicating whether this instance is success.
        /// </summary>
        /// <value>
        /// <c>true</c> if this instance is success; otherwise, <c>false</c>.
        /// </value>
        public bool IsSuccess { get; set; } = false;

        /// <summary>
        /// Actual response if succeed 
        /// </summary>
        /// <value>
        /// Actual response if succeed 
        /// </value>
        public object Data { get; set; } = null;

        /// <summary>
        /// Remark if anythig to convey
        /// </summary>
        /// <value>
        /// Remark if anythig to convey
        /// </value>
        public string Remark { get; set; } = string.Empty;
        /// <summary>
        /// Gets or sets the error message.
        /// </summary>
        /// <value>
        /// The error message.
        /// </value>
        public object ErrorMessage { get; set; } = null;


    }  




[HttpGet]
        public IHttpActionResult Employees()
        {
            Response _res = new Response();
            try
            { 
                DalTest objDal = new DalTest(); 
                _res.Data = objDal.GetTestData();
                _res.IsSuccess = true;
                return Ok<Response>(_res);
            }
            catch (Exception ex)
            {
                _res.IsSuccess = false;
                _res.ErrorMessage = ex;
                return ResponseMessage(Request.CreateResponse(HttpStatusCode.InternalServerError, _res )); 
            } 
        }

You are welcome to give suggestion if any :)

How can I add a new column and data to a datatable that already contains data?

Try this

> dt.columns.Add("ColumnName", typeof(Give the type you want));
> dt.Rows[give the row no like  or  or any no]["Column name in which you want to add data"] = Value;

svn: E155004: ..(path of resource).. is already locked

Still if it doesn't work, just lock all the files and unlock. Now clean up again, It will work.

svn update svn cleanup

PHP $_POST not working?

Instead of using $_POST, use $_REQUEST:

HTML:

<form action="" method="post">
  <input type="text" name="firstname">
  <input type="submit" name="submit" value="Submit">
</form>

PHP:

if(isset($_REQUEST['submit'])){
  $test = $_REQUEST['firstname'];
  echo $test;
}

How to draw vertical lines on a given plot in matplotlib

The standard way to add vertical lines that will cover your entire plot window without you having to specify their actual height is plt.axvline

import matplotlib.pyplot as plt

plt.axvline(x=0.22058956)
plt.axvline(x=0.33088437)
plt.axvline(x=2.20589566)

OR

xcoords = [0.22058956, 0.33088437, 2.20589566]
for xc in xcoords:
    plt.axvline(x=xc)

You can use many of the keywords available for other plot commands (e.g. color, linestyle, linewidth ...). You can pass in keyword arguments ymin and ymax if you like in axes corrdinates (e.g. ymin=0.25, ymax=0.75 will cover the middle half of the plot). There are corresponding functions for horizontal lines (axhline) and rectangles (axvspan).

Cloning an array in Javascript/Typescript

Try this

const returnedTarget = Object.assign(target, source);

and pass empty array to target

in case complex objects this way works for me

$.extend(true, [], originalArray) in case of array

$.extend(true, {}, originalObject) in case of object

What port number does SOAP use?

SOAP (Simple Object Access Protocol) is the communication protocol in the web service scenario.

One benefit of SOAP is that it allowas RPC to execute through a firewall. But to pass through a firewall, you will probably want to use 80. it uses port no.8084 To the firewall, a SOAP conversation on 80 looks like a POST to a web page. However, there are extensions in SOAP which are specifically aimed at the firewall. In the future, it may be that firewalls will be configured to filter SOAP messages. But as of today, most firewalls are SOAP ignorant.

so exclusively open SOAP Port in Firewalls

java.text.ParseException: Unparseable date

Your pattern does not correspond to the input string at all... It is not surprising that it does not work. This would probably work better:

SimpleDateFormat sdf = new SimpleDateFormat("EE MMM dd HH:mm:ss z yyyy",
                                            Locale.ENGLISH);

Then to print with your required format you need a second SimpleDateFormat:

Date parsedDate = sdf.parse(date);
SimpleDateFormat print = new SimpleDateFormat("MMM d, yyyy HH:mm:ss");
System.out.println(print.format(parsedDate));

Notes:

  • you should include the locale as if your locale is not English, the day name might not be recognised
  • IST is ambiguous and can lead to problems so you should use the proper time zone name if possible in your input.

How can I convert a dictionary into a list of tuples?

A simpler one would be

list(dictionary.items())  # list of (key, value) tuples
list(zip(dictionary.values(), dictionary.keys()))  # list of (key, value) tuples

Paste in insert mode?

Paste in Insert Mode

A custom map seems appropriate in this case. This is what I use to paste yanked items in insert mode:

inoremap <Leader>p <ESC>pa

My Leader key here is \; this means hitting \p in insert mode would paste the previously yanked items/lines.

repaint() in Java

You may need to call frame.repaint() as well to force the frame to actually redraw itself. I've had issues before where I tried to repaint a component and it wasn't updating what was displayed until the parent's repaint() method was called.

http post - how to send Authorization header?

Ok. I found problem.

It was not on the Angular side. To be honest, there were no problem at all.

Reason why I was unable to perform my request succesfuly was that my server app was not properly handling OPTIONS request.

Why OPTIONS, not POST? My server app is on different host, then frontend. Because of CORS my browser was converting POST to OPTION: http://restlet.com/blog/2015/12/15/understanding-and-using-cors/

With help of this answer: Standalone Spring OAuth2 JWT Authorization Server + CORS

I implemented proper filter on my server-side app.

Thanks to @Supamiu - the person which fingered me that I am not sending POST at all.

setTimeout in for-loop does not print consecutive values

I had the same problem once this is how I solved it.

Suppose I want 12 delays with an interval of 2 secs

    function animate(i){
         myVar=setTimeout(function(){
            alert(i);
            if(i==12){
              clearTimeout(myVar);
              return;
            }
           animate(i+1)
         },2000)
    }

    var i=1; //i is the start point 1 to 12 that is
    animate(i); //1,2,3,4..12 will be alerted with 2 sec delay

PHP XML how to output nice format

With a SimpleXml object, you can simply

$domxml = new DOMDocument('1.0');
$domxml->preserveWhiteSpace = false;
$domxml->formatOutput = true;
/* @var $xml SimpleXMLElement */
$domxml->loadXML($xml->asXML());
$domxml->save($newfile);

$xml is your simplexml object

So then you simpleXml can be saved as a new file specified by $newfile

How to Update Date and Time of Raspberry Pi With out Internet

You will need to configure your Win7 PC as a Time Server, and then configure the RasPi to connect to it for NTP services.

Configure Win7 as authoritative time server. Configure RasPi time server lookup.

Loop Through All Subfolders Using VBA

And to complement Rich's recursive answer, a non-recursive method.

Public Sub NonRecursiveMethod()
    Dim fso, oFolder, oSubfolder, oFile, queue As Collection

    Set fso = CreateObject("Scripting.FileSystemObject")
    Set queue = New Collection
    queue.Add fso.GetFolder("your folder path variable") 'obviously replace

    Do While queue.Count > 0
        Set oFolder = queue(1)
        queue.Remove 1 'dequeue
        '...insert any folder processing code here...
        For Each oSubfolder In oFolder.SubFolders
            queue.Add oSubfolder 'enqueue
        Next oSubfolder
        For Each oFile In oFolder.Files
            '...insert any file processing code here...
        Next oFile
    Loop

End Sub

You can use a queue for FIFO behaviour (shown above), or you can use a stack for LIFO behaviour which would process in the same order as a recursive approach (replace Set oFolder = queue(1) with Set oFolder = queue(queue.Count) and replace queue.Remove(1) with queue.Remove(queue.Count), and probably rename the variable...)

Spring Boot JPA - configuring auto reconnect

As some people already pointed out, spring-boot 1.4+, has specific namespaces for the four connections pools. By default, hikaricp is used in spring-boot 2+. So you will have to specify the SQL here. The default is SELECT 1. Here's what you would need for DB2 for example: spring.datasource.hikari.connection-test-query=SELECT current date FROM sysibm.sysdummy1

Caveat: If your driver supports JDBC4 we strongly recommend not setting this property. This is for "legacy" drivers that do not support the JDBC4 Connection.isValid() API. This is the query that will be executed just before a connection is given to you from the pool to validate that the connection to the database is still alive. Again, try running the pool without this property, HikariCP will log an error if your driver is not JDBC4 compliant to let you know. Default: none

How to suppress binary file matching results in grep

There are three options, that you can use. -I is to exclude binary files in grep. Other are for line numbers and file names.

grep -I -n -H 


-I -- process a binary file as if it did not contain matching data; 
-n -- prefix each line of output with the 1-based line number within its input file
-H -- print the file name for each match

So this might be a way to run grep:

grep -InH your-word *

How to style a div to have a background color for the entire width of the content, and not just for the width of the display?

black magic:

<style>
body { float:left;}
.success { background-color: #ccffcc;}
</style>

If anyone has a clear explanation of why this works, please comment. I think it has something to do with a side effect of the float that removes the constraint that the body must fit into the page width.

JavaScript - Get Browser Height

There's a simpler way than a whole bunch of if statements. Use the or (||) operator.

function getBrowserDimensions() {
  return {
    width: (window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth),
    height: (window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight)
  };
}

var browser_dims = getBrowserDimensions();

alert("Width = " + browser_dims.width + "\nHeight = " + browser_dims.height);

Simple bubble sort c#

int[] arr = { 800, 11, 50, 771, 649, 770, 240, 9 };

int temp = 0;

for (int write = 0; write < arr.Length; write++)
{
    for (int sort = 0; sort < arr.Length - 1 - write ; sort++)
    {
        if (arr[sort] > arr[sort + 1])
        {
            temp = arr[sort + 1];
            arr[sort + 1] = arr[sort];
            arr[sort] = temp;
        }
    }
}

for (int i = 0; i < arr.Length; i++) Console.Write(arr[i] + " ");

Console.ReadKey();

The developers of this app have not set up this app properly for Facebook Login?

do setup by following bellow link and domain name you need to mention as like wht you have mentioned in facebook app domain name.

Go to https://developers.facebook.com/

Click on the Apps menu on the top bar.

Why do Python's math.ceil() and math.floor() operations return floats instead of integers?

As pointed out by other answers, in python they return floats probably because of historical reasons to prevent overflow problems. However, they return integers in python 3.

>>> import math
>>> type(math.floor(3.1))
<class 'int'>
>>> type(math.ceil(3.1))
<class 'int'>

You can find more information in PEP 3141.

How to set up gradle and android studio to do release build?

in the latest version of android studio, you can just do:

./gradlew assembleRelease

or aR for short. This will produce an unsigned release apk. Building a signed apk can be done similarly or you can use Build -> Generate Signed Apk in Android Studio.

See the docs here

Here is my build.gradle for reference:

buildscript {
  repositories {
    mavenCentral()
  }
  dependencies {
    classpath 'com.android.tools.build:gradle:0.5.+'
  }
}
apply plugin: 'android'

dependencies {
  compile fileTree(dir: 'libs', include: '*.jar')
}

android {
compileSdkVersion 17
buildToolsVersion "17.0.0"

sourceSets {
    main {
        manifest.srcFile 'AndroidManifest.xml'
        java.srcDirs = ['src']
        resources.srcDirs = ['src']
        aidl.srcDirs = ['src']
        renderscript.srcDirs = ['src']
        res.srcDirs = ['res']
        assets.srcDirs = ['assets']
    }

    // Move the tests to tests/java, tests/res, etc...
    instrumentTest.setRoot('tests')

    // Move the build types to build-types/<type>
    // For instance, build-types/debug/java, build-types/debug/AndroidManifest.xml, ...
    // This moves them out of them default location under src/<type>/... which would
    // conflict with src/ being used by the main source set.
    // Adding new build types or product flavors should be accompanied
    // by a similar customization.
    debug.setRoot('build-types/debug')
    release.setRoot('build-types/release')

}

buildTypes {
    release {

    }
}

How to import local packages in go?

Well, I figured out the problem. Basically Go starting path for import is $HOME/go/src

So I just needed to add myapp in front of the package names, that is, the import should be:

import (
    "log"
    "net/http"
    "myapp/common"
    "myapp/routers"
)

Maven – Always download sources and javadocs

Not sure, but you should be able to do something by setting a default active profile in your settings.xml

See

See http://maven.apache.org/guides/introduction/introduction-to-profiles.html

Fixed position but relative to container

Actually this is possible and the accepted answer only deals with centralising, which is straightforward enough. Also you really don't need to use JavaScript.

This will let you deal with any scenario:

Set everything up as you would if you want to position: absolute inside a position: relative container, and then create a new fixed position div inside the div with position: absolute, but do not set its top and left properties. It will then be fixed wherever you want it, relative to the container.

For example:

_x000D_
_x000D_
/* Main site body */_x000D_
.wrapper {_x000D_
    width: 940px;_x000D_
    margin: 0 auto;_x000D_
    position: relative; /* Ensure absolute positioned child elements are relative to this*/_x000D_
}_x000D_
_x000D_
/* Absolute positioned wrapper for the element you want to fix position */_x000D_
.fixed-wrapper {_x000D_
    width: 220px;_x000D_
    position: absolute;_x000D_
    top: 0;_x000D_
    left: -240px; /* Move this out to the left of the site body, leaving a 20px gutter */_x000D_
}_x000D_
_x000D_
/* The element you want to fix the position of */_x000D_
.fixed {_x000D_
    width: 220px;_x000D_
    position: fixed;_x000D_
    /* Do not set top / left! */_x000D_
}
_x000D_
<div class="wrapper">_x000D_
    <div class="fixed-wrapper">_x000D_
        <div class="fixed">_x000D_
            Content in here will be fixed position, but 240px to the left of the site body._x000D_
        </div>_x000D_
    </div>_x000D_
</div>
_x000D_
_x000D_
_x000D_

Sadly, I was hoping this thread might solve my issue with Android's WebKit rendering box-shadow blur pixels as margins on fixed position elements, but it seems it's a bug.
Anyway, I hope this helps!

How to do case insensitive search in Vim

You can use the \c escape sequence anywhere in the pattern. For example:

/\ccopyright or /copyright\c or even /copyri\cght

To do the inverse (case sensitive matching), use \C (capital C) instead.

Any way to clear python's IDLE window?

ctrl + L clears the screen on Ubuntu Linux.

Override valueof() and toString() in Java enum

You can use a static Map in your enum that maps Strings to enum constants. Use it in a 'getEnum' static method. This skips the need to iterate through the enums each time you want to get one from its String value.

public enum RandomEnum {

    StartHere("Start Here"),
    StopHere("Stop Here");

    private final String strVal;
    private RandomEnum(String strVal) {
        this.strVal = strVal;
    }

    public static RandomEnum getEnum(String strVal) {
        if(!strValMap.containsKey(strVal)) {
            throw new IllegalArgumentException("Unknown String Value: " + strVal);
        }
        return strValMap.get(strVal);
    }

    private static final Map<String, RandomEnum> strValMap;
    static {
        final Map<String, RandomEnum> tmpMap = Maps.newHashMap();
        for(final RandomEnum en : RandomEnum.values()) {
            tmpMap.put(en.strVal, en);
        }
        strValMap = ImmutableMap.copyOf(tmpMap);
    }

    @Override
    public String toString() {
        return strVal;
    }
}

Just make sure the static initialization of the map occurs below the declaration of the enum constants.

BTW - that 'ImmutableMap' type is from the Google guava API, and I definitely recommend it in cases like this.


EDIT - Per the comments:

  1. This solution assumes that each assigned string value is unique and non-null. Given that the creator of the enum can control this, and that the string corresponds to the unique & non-null enum value, this seems like a safe restriction.
  2. I added the 'toSTring()' method as asked for in the question

How to filter an array from all elements of another array

You can use the filter and then for the filter function use a reduction of the filtering array which checks and returns true when it finds a match then invert on return (!). The filter function is called once per element in the array. You are not doing a comparison of any of the elements in the function in your post.

_x000D_
_x000D_
var a1 = [1, 2, 3, 4],_x000D_
  a2 = [2, 3];_x000D_
_x000D_
var filtered = a1.filter(function(x) {_x000D_
  return !a2.reduce(function(y, z) {_x000D_
    return x == y || x == z || y == true;_x000D_
  })_x000D_
});_x000D_
_x000D_
document.write(filtered);
_x000D_
_x000D_
_x000D_

How to remove old Docker containers

You can stop the docker container and once it is stopped you can remove the container.

Stop the container:

$ docker stop "containerID" - you can also mention the first two letters of the container ID, and it works.

Remove the container

$ docker rm "containerID" - again you can also mention the first two letters of the container

If these command do not let you stop/remove the containers, m,ake sure you have sudo access to docker host.

The property 'value' does not exist on value of type 'HTMLElement'

Also for anyone using properties such as Props or Refs without your "DocgetId's" then you can:

("" as HTMLInputElement).value;

Where the inverted quotes is your props value so an example would be like so:

var val = (this.refs.newText as HTMLInputElement).value;
alert("Saving this:" + val);

How to filter wireshark to see only dns queries that are sent/received from/by my computer?

Rather than using a DisplayFilter you could use a very simple CaptureFilter like

port 53

See the "Capture only DNS (port 53) traffic" example on the CaptureFilters wiki.

How to create a List with a dynamic object type

It appears you might be a bit confused as to how the .Add method works. I will refer directly to your code in my explanation.

Basically in C#, the .Add method of a List of objects does not COPY new added objects into the list, it merely copies a reference to the object (it's address) into the List. So the reason every value in the list is pointing to the same value is because you've only created 1 new DyObj. So your list essentially looks like this.

DyObjectsList[0] = &DyObj; // pointing to DyObj
DyObjectsList[1] = &DyObj; // pointing to the same DyObj
DyObjectsList[2] = &DyObj; // pointing to the same DyObj

...

The easiest way to fix your code is to create a new DyObj for every .Add. Putting the new inside of the block with the .Add would accomplish this goal in this particular instance.

var DyObjectsList = new List<dynamic>; 
if (condition1) { 
    dynamic DyObj = new ExpandoObject(); 
    DyObj.Required = true; 
    DyObj.Message = "Message 1"; 
    DyObjectsList .Add(DyObj); 
} 
if (condition2) { 
    dynamic DyObj = new ExpandoObject(); 
    DyObj.Required = false; 
    DyObj.Message = "Message 2"; 
    DyObjectsList .Add(DyObj); 
} 

your resulting List essentially looks like this

DyObjectsList[0] = &DyObj0; // pointing to a DyObj
DyObjectsList[1] = &DyObj1; // pointing to a different DyObj
DyObjectsList[2] = &DyObj2; // pointing to another DyObj

Now in some other languages this approach wouldn't work, because as you leave the block, the objects declared in the scope of the block could go out of scope and be destroyed. Thus you would be left with a collection of pointers, pointing to garbage.

However in C#, if a reference to the new DyObjs exists when you leave the block (and they do exist in your List because of the .Add operation) then C# does not release the memory associated with that pointer. Therefore the Objects you created in that block persist and your List contains pointers to valid objects and your code works.

Delete all files in directory (but not directory) - one liner solution

rm -rf was much more performant than FileUtils.cleanDirectory.

Not a one-liner solution but after extensive benchmarking, we found that using rm -rf was multiple times faster than using FileUtils.cleanDirectory.

Of course, if you have a small or simple directory, it won't matter but in our case we had multiple gigabytes and deeply nested sub directories where it would take over 10 minutes with FileUtils.cleanDirectory and only 1 minute with rm -rf.

Here's our rough Java implementation to do that:

// Delete directory given and all subdirectories and files (i.e. recursively).
//
static public boolean clearDirectory( File file ) throws IOException, InterruptedException {

    if ( file.exists() ) {

        String deleteCommand = "rm -rf " + file.getAbsolutePath();
        Runtime runtime = Runtime.getRuntime();

        Process process = runtime.exec( deleteCommand );
        process.waitFor();

        file.mkdirs(); // Since we only want to clear the directory and not delete it, we need to re-create the directory.

        return true;
    }

    return false;

}

Worth trying if you're dealing with large or complex directories.

Unresolved external symbol in object files

I had an error where my project was compiled as x64 project. and I've used a Library that was compiled as x86.

I've recompiled the library as x64 and it solved it.

What does question mark and dot operator ?. mean in C# 6.0?

This is relatively new to C# which makes it easy for us to call the functions with respect to the null or non-null values in method chaining.

old way to achieve the same thing was:

var functionCaller = this.member;
if (functionCaller!= null)
    functionCaller.someFunction(var someParam);

and now it has been made much easier with just:

member?.someFunction(var someParam);

I strongly recommend this doc page.

WebAPI Multiple Put/Post parameters

Natively WebAPI doesn't support binding of multiple POST parameters. As Colin points out there are a number of limitations that are outlined in my blog post he references.

There's a workaround by creating a custom parameter binder. The code to do this is ugly and convoluted, but I've posted code along with a detailed explanation on my blog, ready to be plugged into a project here:

Passing multiple simple POST Values to ASP.NET Web API

Convert array of strings into a string in Java

Try the Arrays.deepToString method.

Returns a string representation of the "deep contents" of the specified array. If the array contains other arrays as elements, the string representation contains their contents and so on. This method is designed for converting multidimensional arrays to strings

MySQL 8.0 - Client does not support authentication protocol requested by server; consider upgrading MySQL client

For existing mysql 8.0 installs on Windows 10 mysql,

  1. launch installer,

  2. click "Reconfigure" under QuickAction (to the left of MySQL Server), then

  3. click next to advance through the next 2 screens until arriving

  4. at "Authentication Method", select "Use Legacy Authentication Method (Retain MySQL 5.x compatibility"

  5. Keep clicking until install is complete

How can I replace a newline (\n) using sed?

gnu sed has an option -z for null separated records (lines). You can just call:

sed -z 's/\n/ /g'

How can I save a screenshot directly to a file in Windows?

Is this possible:

  1. Press Alt PrintScreen
  2. Open a folder
  3. Right click -> paste screenshot

Example:

Benchmark result window is open, take a screenshot. Open C:\Benchmarks Right click -> Paste screenshot A file named screenshot00x.jpg appears, with text screenshot00x selected. Type Overclock5

Thats it. No need to open anything. If you do not write anything, default name stays.

java.lang.OutOfMemoryError: bitmap size exceeds VM budget - Android

To avoid this problem you can use native method Bitmap.recycle() before null-ing Bitmap object (or setting another value). Example:

public final void setMyBitmap(Bitmap bitmap) {
  if (this.myBitmap != null) {
    this.myBitmap.recycle();
  }
  this.myBitmap = bitmap;
}

And next you can change myBitmap w/o calling System.gc() like:

setMyBitmap(null);    
setMyBitmap(anotherBitmap);

Read only file system on Android

Copy files to the SD-card?

Well, I assume you like to copy data to the Sd-card from the developers computer? You might have rooted the devise and made the area you address available?) I had about the same problem to upload data files for my application(Android Studio 1.3.2 in Win7), but.

  • First the adb command-shell has to be found in th path: PATH=%PATH%;C:\Users\XXXXX\AppData\Local\Android\sdk\platform-tools (the folder AppData is hidden, so you have to set the folder setup not hiding concealed files and folder to find it, Path works regardless)
  • You have to spell the folder path right or you get a read-only error message, most likely it must start with /sdcard or it is read only area. As soon as I did no problem pushing the file to the emulator.

So for instance the the adb command can look like this:

adb push C:\testdata\t.txt /sdcard/download/t.txt

What is the correct syntax for 'else if'?

since olden times, the correct syntax for if/else if in Python is elif. By the way, you can use dictionary if you have alot of if/else.eg

d={"1":"1a","2":"2a"}
if not a in d: print("3a")
else: print (d[a])

For msw, example of executing functions using dictionary.

def print_one(arg=None):
    print "one"

def print_two(num):
    print "two %s" % num

execfunctions = { 1 : (print_one, ['**arg'] ) , 2 : (print_two , ['**arg'] )}
try:
    execfunctions[1][0]()
except KeyError,e:
    print "Invalid option: ",e

try:
    execfunctions[2][0]("test")
except KeyError,e:
    print "Invalid option: ",e
else:
    sys.exit()

How can I get a favicon to show up in my django app?

Best practices :

Contrary to what you may think, the favicon can be of any size and of any image type. Follow this link for details.

Not putting a link to your favicon can slow down the page load.

In a django project, suppose the path to your favicon is :

myapp/static/icons/favicon.png

in your django templates (preferably in the base template), add this line to head of the page :

<link rel="shortcut icon" href="{%  static 'icons/favicon.png' %}">

Note :

We suppose, the static settings are well configured in settings.py.

Maintain/Save/Restore scroll position when returning to a ListView

BEST SOLUTION IS:

// save index and top position
int index = mList.getFirstVisiblePosition();
View v = mList.getChildAt(0);
int top = (v == null) ? 0 : (v.getTop() - mList.getPaddingTop());

// ...

// restore index and position
mList.post(new Runnable() {
    @Override
    public void run() {
      mList.setSelectionFromTop(index, top);
   }
});

YOU MUST CALL IN POST AND IN THREAD!

Oracle: SQL select date with timestamp

Answer provided by Nicholas Krasnov

SELECT *
FROM BOOKING_SESSION
WHERE TO_CHAR(T_SESSION_DATETIME, 'DD-MM-YYYY') ='20-03-2012';

Is nested function a good approach when required by only one function?

A function inside of a function is commonly used for closures.

(There is a lot of contention over what exactly makes a closure a closure.)

Here's an example using the built-in sum(). It defines start once and uses it from then on:

def sum_partial(start):
    def sum_start(iterable):
        return sum(iterable, start)
    return sum_start

In use:

>>> sum_with_1 = sum_partial(1)
>>> sum_with_3 = sum_partial(3)
>>> 
>>> sum_with_1
<function sum_start at 0x7f3726e70b90>
>>> sum_with_3
<function sum_start at 0x7f3726e70c08>
>>> sum_with_1((1,2,3))
7
>>> sum_with_3((1,2,3))
9

Built-in python closure

functools.partial is an example of a closure.

From the python docs, it's roughly equivalent to:

def partial(func, *args, **keywords):
    def newfunc(*fargs, **fkeywords):
        newkeywords = keywords.copy()
        newkeywords.update(fkeywords)
        return func(*(args + fargs), **newkeywords)
    newfunc.func = func
    newfunc.args = args
    newfunc.keywords = keywords
    return newfunc

(Kudos to @user225312 below for the answer. I find this example easier to figure out, and hopefully will help answer @mango's comment.)

How to parse a date?

How about getSelectedDate? Anyway, specifically on your code question, the problem is with this line:

new SimpleDateFormat("yyyy-MM-dd");

The string that goes in the constructor has to match the format of the date. The documentation for how to do that is here. Looks like you need something close to "EEE MMM d HH:mm:ss zzz yyyy"

How to add a new audio (not mixing) into a video using ffmpeg?

If the input video has multiple audio tracks and you need to add one more then use the following command:

ffmpeg -i input_video_with_audio.avi -i new_audio.ac3 -map 0 -map 1 -codec copy output_video.avi

-map 0 means to copy (include) all streams from the first input file (input_video_with_audio.avi) and -map 1 means to include all streams (in this case one) from the second input file (new_audio.ac3).

Html.BeginForm and adding properties

I know this is old but you could create a custom extension if you needed to create that form over and over:

public static MvcForm BeginMultipartForm(this HtmlHelper htmlHelper)
{
    return htmlHelper.BeginForm(null, null, FormMethod.Post, 
     new Dictionary<string, object>() { { "enctype", "multipart/form-data" } });
}

Usage then just becomes

<% using(Html.BeginMultipartForm()) { %>

How to paginate with Mongoose in Node.js?

If you are using mongoose as a source for a restful api have a look at 'restify-mongoose' and its queries. It has exactly this functionality built in.

Any query on a collection provides headers that are helpful here

test-01:~$ curl -s -D - localhost:3330/data?sort=-created -o /dev/null
HTTP/1.1 200 OK
link: </data?sort=-created&p=0>; rel="first", </data?sort=-created&p=1>; rel="next", </data?sort=-created&p=134715>; rel="last"
.....
Response-Time: 37

So basically you get a generic server with a relatively linear load time for queries to collections. That is awesome and something to look at if you want to go into a own implementation.

Determine on iPhone if user has enabled push notifications

In the latest version of iOS this method is now deprecated. To support both iOS 7 and iOS 8 use:

UIApplication *application = [UIApplication sharedApplication];

BOOL enabled;

// Try to use the newer isRegisteredForRemoteNotifications otherwise use the enabledRemoteNotificationTypes.
if ([application respondsToSelector:@selector(isRegisteredForRemoteNotifications)])
{
    enabled = [application isRegisteredForRemoteNotifications];
}
else
{
    UIRemoteNotificationType types = [application enabledRemoteNotificationTypes];
    enabled = types & UIRemoteNotificationTypeAlert;
}

Loading all images using imread from a given folder

To add onto the answer from Rishabh and make it able to handle files that are not images that are found in the folder.

import matplotlib.image as mpimg

images = []
folder = './your/folder/'
for filename in os.listdir(folder):
    try:
        img = mpimg.imread(os.path.join(folder, filename))
        if img is not None:
            images.append(img)
    except:
        print('Cant import ' + filename)
images = np.asarray(images)

React Native add bold or italics to single words in <Text> field

For a more web-like feel:

const B = (props) => <Text style={{fontWeight: 'bold'}}>{props.children}</Text>
<Text>I am in <B>bold</B> yo.</Text>

Calculate a MD5 hash from a string

I suppose it is better to use UTF-8 encoding in the string MD5.

public static string MD5(this string s)
{
    using (var provider = System.Security.Cryptography.MD5.Create())
    {
        StringBuilder builder = new StringBuilder();                           

        foreach (byte b in provider.ComputeHash(Encoding.UTF8.GetBytes(s)))
            builder.Append(b.ToString("x2").ToLower());

        return builder.ToString();
    }
}

mongodb count num of distinct values per field/key

With MongoDb 3.4.4 and newer, you can leverage the use of $arrayToObject operator and a $replaceRoot pipeline to get the counts.

For example, suppose you have a collection of users with different roles and you would like to calculate the distinct counts of the roles. You would need to run the following aggregate pipeline:

db.users.aggregate([
    { "$group": {
        "_id": { "$toLower": "$role" },
        "count": { "$sum": 1 }
    } },
    { "$group": {
        "_id": null,
        "counts": {
            "$push": { "k": "$_id", "v": "$count" }
        }
    } },
    { "$replaceRoot": {
        "newRoot": { "$arrayToObject": "$counts" }
    } }    
])

Example Output

{
    "user" : 67,
    "superuser" : 5,
    "admin" : 4,
    "moderator" : 12
}

How to read specific lines from a file (by line number)?

def getitems(iterable, items):
  items = list(items) # get a list from any iterable and make our own copy
                      # since we modify it
  if items:
    items.sort()
    for n, v in enumerate(iterable):
      if n == items[0]:
        yield v
        items.pop(0)
        if not items:
          break

print list(getitems(open("/usr/share/dict/words"), [25, 29]))
# ['Abelson\n', 'Abernathy\n']
# note that index 25 is the 26th item

CSS3 Spin Animation

As of latest Chrome/FF and on IE11 there's no need for -ms/-moz/-webkit prefix. Here's a shorter code (based on previous answers):

div {
    margin: 20px;
    width: 100px;
    height: 100px;
    background: #f00;

    /* The animation part: */
    animation-name: spin;
    animation-duration: 4000ms;
    animation-iteration-count: infinite;
    animation-timing-function: linear;
}
@keyframes spin {
    from {transform:rotate(0deg);}
    to {transform:rotate(360deg);}
}

Live Demo: http://jsfiddle.net/9Ryvs/3057/

SQL update trigger only when column is modified

Whenever a record has updated a record is "deleted". Here is my example:

ALTER TRIGGER [dbo].[UpdatePhyDate]
   ON  [dbo].[M_ContractDT1]
   AFTER UPDATE
AS 
BEGIN
    -- on ContarctDT1 PhyQty is updated 
    -- I want system date in Phytate automatically saved
    SET NOCOUNT ON;

    declare @dt1ky as int   

    if(update(Phyqty))
    begin
        select @dt1ky = dt1ky from deleted

        update M_ContractDT1 set PhyDate=GETDATE() where Dt1Ky=  @dt1ky     

    end

END

It works fine

Java double.MAX_VALUE?

this states that Account.deposit(Double.MAX_VALUE); it is setting deposit value to MAX value of Double dataType.to procced for running tests.

Send email by using codeigniter library via localhost

$insert = $this->db->insert('email_notification', $data);
                $this->session->set_flashdata("msg", "<div class='alert alert-success'> Cafe has been added Successfully.</div>");

                //require ("plugins/mailer/PHPMailerAutoload.php");
                $mail = new PHPMailer;
                $mail->SMTPOptions = array(
                    'ssl' => array(
                    'verify_peer' => false,
                    'verify_peer_name' => false,
                    'allow_self_signed' => true,
                ),
                );

                $message="
                     Your Account Has beed created successfully by Admin:
                    Username: ".$this->input->post('username')." <br><br>
                    Email: ".$this->input->post('sender_email')." <br><br>
                    Regargs<br>
                    <div class='background-color:#666;color:#fff;padding:6px;
                    text-align:center;'>
                         Bookly Admin.
                    </div>
                ";
                $mail->isSMTP(); // Set mailer to use SMTP
                $mail->Host = 'smtp.gmail.com'; // Specify main and backup SMTP servers
                $mail->SMTPAuth = true; 
                $subject = "Hello  ".$this->input->post('username');
                $mail->SMTDebug=2;
                $email = $this->input->post('sender_email'); //this email is user email
                $from_label = "Account Creation";
                $mail->Username = 'your email'; // SMTP username
                $mail->Password = 'password'; // SMTP password
                $mail->SMTPSecure = 'ssl'; // Enable TLS encryption, `ssl` also accepted
                $mail->Port = 465;
                $mail->setFrom($from_label);
                $mail->addAddress($email, 'Bookly Admin');
                $mail->isHTML(true);
                $mail->Subject = $subject;
                $mail->Body = $message;
                $mail->AltBody = 'This is the body in plain text for non-HTML mail clients';
             if($mail->send()){

                  }

Why do I need to override the equals and hashCode methods in Java?

class A {
    int i;
    // Hashing Algorithm
    if even number return 0 else return 1
    // Equals Algorithm,
    if i = this.i return true else false
}
  • put('key','value') will calculate the hash value using hashCode() to determine the bucket and uses equals() method to find whether the value is already present in the Bucket. If not it will added else it will be replaced with current value
  • get('key') will use hashCode() to find the Entry (bucket) first and equals() to find the value in Entry

if Both are overridden,

Map<A>

Map.Entry 1 --> 1,3,5,...
Map.Entry 2 --> 2,4,6,...

if equals is not overridden

Map<A>

Map.Entry 1 --> 1,3,5,...,1,3,5,... // Duplicate values as equals not overridden
Map.Entry 2 --> 2,4,6,...,2,4,..

If hashCode is not overridden

Map<A>

Map.Entry 1 --> 1
Map.Entry 2 --> 2
Map.Entry 3 --> 3
Map.Entry 4 --> 1
Map.Entry 5 --> 2
Map.Entry 6 --> 3 // Same values are Stored in different hasCodes violates Contract 1
So on...

HashCode Equal Contract

  1. Two keys equal according to equal method should generate same hashCode
  2. Two Keys generating same hashCode need not be equal (In above example all even numbers generate same hash Code)

Git pull a certain branch from GitHub

I did

git branch -f new_local_branch_name origin/remote_branch_name

Instead of

git branch -f new_local_branch_name upstream/remote_branch_name

As suggested by @innaM. When I used the upstream version, it said 'fatal: Not a valid object name: 'upstream/remote_branch_name''. I did not do git fetch origin as a comment suggested, but instead simply replaced upstream with origin. I guess they are equivalent.

Unable to start Genymotion Virtual Device - Virtualbox Host Only Ethernet Adapter Failed to start

In Mac, Open Oracle Virtual Box and Goto VirtualBox -> Preferences -> Network. Select the tab'Host Only Networks' & delete vboxnet0. It will be recreated next time you launch genymotion emulator.

Change Placeholder Text using jQuery

try this

$('#Selector_ID').attr("placeholder", "your Placeholder");

Why do I get an UnsupportedOperationException when trying to remove an element from a List?

Following is snippet of code from Arrays

public static <T> List<T> asList(T... a) {
        return new ArrayList<>(a);
    }

    /**
     * @serial include
     */
    private static class ArrayList<E> extends AbstractList<E>
        implements RandomAccess, java.io.Serializable
    {
        private static final long serialVersionUID = -2764017481108945198L;
        private final E[] a;

so what happens is that when asList method is called then it returns list of its own private static class version which does not override add funcion from AbstractList to store element in array. So by default add method in abstract list throws exception.

So it is not regular array list.

When should I use "this" in a class?

The second important use of this (beside hiding with a local variable as many answers already say) is when accessing an outer instance from a nested non-static class:

public class Outer {
  protected int a;

  public class Inner {
    protected int a;

    public int foo(){
      return Outer.this.a;
    }

    public Outer getOuter(){
      return Outer.this;
    }
  }
}

How to uncheck checked radio button

This simple script allows you to uncheck an already checked radio button. Works on all javascript enabled browsers.

_x000D_
_x000D_
var allRadios = document.getElementsByName('re');_x000D_
var booRadio;_x000D_
var x = 0;_x000D_
for(x = 0; x < allRadios.length; x++){_x000D_
  allRadios[x].onclick = function() {_x000D_
    if(booRadio == this){_x000D_
      this.checked = false;_x000D_
      booRadio = null;_x000D_
    } else {_x000D_
      booRadio = this;_x000D_
    }_x000D_
  };_x000D_
}
_x000D_
<input type='radio' class='radio-button' name='re'>_x000D_
<input type='radio' class='radio-button' name='re'>_x000D_
<input type='radio' class='radio-button' name='re'>
_x000D_
_x000D_
_x000D_

What does $ mean before a string?

$ is short-hand for String.Format and is used with string interpolations, which is a new feature of C# 6. As used in your case, it does nothing, just as string.Format() would do nothing.

It is comes into its own when used to build strings with reference to other values. What previously had to be written as:

var anInt = 1;
var aBool = true;
var aString = "3";
var formated = string.Format("{0},{1},{2}", anInt, aBool, aString);

Now becomes:

var anInt = 1;
var aBool = true;
var aString = "3";
var formated = $"{anInt},{aBool},{aString}";

There's also an alternative - less well known - form of string interpolation using $@ (the order of the two symbols is important). It allows the features of a @"" string to be mixed with $"" to support string interpolations without the need for \\ throughout your string. So the following two lines:

var someDir = "a";
Console.WriteLine($@"c:\{someDir}\b\c");

will output:

c:\a\b\c

Find if variable is divisible by 2

You can also:

if (x & 1)
 itsOdd();
else
 itsEven();

Extension mysqli is missing, phpmyadmin doesn't work

Had the very same problem, but in my case the reason was update of Ubuntu and php version - from 18.04 and php-7.2 up to 20.04 and php-7.4.

The Nginx server was the same, so in my /etc/nginx/sites-available/default was old data:

server {
  location /pma {
    location ~ ^/pma/(.+\.php)$ {
      fastcgi_pass unix:/run/php/php7.2-fpm.sock;
    }
  }
}

I could not get phpmyadmin to work with any of php.ini changes and all answers from this thread, but at some moment I had opened the /etc/nginx/sites-available/default and realised, that I still had old version of php. So I just changed it to

fastcgi_pass unix:/run/php/php7.4-fpm.sock;

and the issue was gone, phpmyadmin magically started to work without any mysqli-file complaint. I even double checked it, but yeap, that's how it works - if you have wrong version for php-fpm.sock in your nginx config file, your phpmyadmin will not work, but the shown reason will be 'The mysqli extension is missing'

Is there a Python equivalent to Ruby's string interpolation?

import inspect
def s(template, **kwargs):
    "Usage: s(string, **locals())"
    if not kwargs:
        frame = inspect.currentframe()
        try:
            kwargs = frame.f_back.f_locals
        finally:
            del frame
        if not kwargs:
            kwargs = globals()
    return template.format(**kwargs)

Usage:

a = 123
s('{a}', locals()) # print '123'
s('{a}') # it is equal to the above statement: print '123'
s('{b}') # raise an KeyError: b variable not found

PS: performance may be a problem. This is useful for local scripts, not for production logs.

Duplicated:

Why would Oracle.ManagedDataAccess not work when Oracle.DataAccess does?

I received the same error message. To resolve this I just replaced the Oracle.ManagedDataAccess assembly with the older Oracle.DataAccess assembly. This solution may not work if you require new features found in the new assembly. In my case I have many more higher priority issues then trying to configure the new Oracle assembly.

Undefined symbols for architecture i386: _OBJC_CLASS_$_SKPSMTPMessage", referenced from: error

I got this message when I drag and dropped some source files from another project. When I deleted them and then added them via the "Add Files..." from the File menu, it built without the error.

Struct Constructor in C++?

Note that there is one interesting difference (at least with the MS C++ compiler):


If you have a plain vanilla struct like this

struct MyStruct {
   int id;
   double x;
   double y;
} MYSTRUCT;

then somewhere else you might initialize an array of such objects like this:

MYSTRUCT _pointList[] = { 
   { 1, 1.0, 1.0 }, 
   { 2, 1.0, 2.0 }, 
   { 3, 2.0, 1.0 }
};

however, as soon as you add a user-defined constructor to MyStruct such as the ones discussed above, you'd get an error like this:

    'MyStruct' : Types with user defined constructors are not aggregate
     <file and line> : error C2552: '_pointList' : non-aggregates cannot 
     be initialized with initializer list.

So that's at least one other difference between a struct and a class. This kind of initialization may not be good OO practice, but it appears all over the place in the legacy WinSDK c++ code that I support. Just so you know...

Error: Execution failed for task ':app:clean'. Unable to delete file

In Android Studio 3.0, I had the same issue. This fixed it:

  1. Close Studio
  2. Delete projectRoot/build/ and projectRoot/app/build/
  3. Restart Studio

Write a mode method in Java to find the most frequently occurring element in an array

    Arrays.sort(arr);
    int max=0,mode=0,count=0;
    for(int i=0;i<N;i=i+count) {
        count = 1;
        for(int j=i+1; j<N; j++) {
            if(arr[i] == arr[j])
                count++;
        }
        if(count>max) {
            max=count;
            mode = arr[i];
        }
    }

Remove scrollbar from iframe

Just Add scrolling="no" and seamless="seamless" attributes to iframe tag. like this:-

 1. XHTML => scrolling="no"
 2. HTML5 => seamless="seamless"

UPDATE:

seamless attribute has been removed in all major browsers

Textfield with only bottom border

See this JSFiddle

_x000D_
_x000D_
 input[type="text"]_x000D_
    {_x000D_
        border: 0;_x000D_
        border-bottom: 1px solid red;_x000D_
        outline: 0;_x000D_
    }
_x000D_
<form>_x000D_
        <input type="text" value="See! ONLY BOTTOM BORDER!" />_x000D_
    </form>
_x000D_
_x000D_
_x000D_

How do you setLayoutParams() for an ImageView?

You need to set the LayoutParams of the ViewGroup the ImageView is sitting in. For example if your ImageView is inside a LinearLayout, then you create a

LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(30, 30);
yourImageView.setLayoutParams(layoutParams);

This is because it's the parent of the View that needs to know what size to allocate to the View.

How can I have a newline in a string in sh?

Echo is so nineties and so fraught with perils that its use should result in core dumps no less than 4GB. Seriously, echo's problems were the reason why the Unix Standardization process finally invented the printf utility, doing away with all the problems.

So to get a newline in a string:

FOO="hello
world"
BAR=$(printf "hello\nworld\n") # Alternative; note: final newline is deleted
printf '<%s>\n' "$FOO"
printf '<%s>\n' "$BAR"

There! No SYSV vs BSD echo madness, everything gets neatly printed and fully portable support for C escape sequences. Everybody please use printf now and never look back.

Adding a directory to the PATH environment variable in Windows

On Windows 10, I was able to search for set path environment variable and got these instructions:

  1. From the desktop, right-click the very bottom-left corner of the screen to get the Power User Task Menu.
  2. From the Power User Task Menu, click System.
  3. In the Settings window, scroll down to the Related settings section and click the System info link.
  4. In the System window, click the Advanced system settings link in the left navigation panel.
  5. In the System Properties window, click the Advanced tab, then click the Environment Variables button near the bottom of that tab.
  6. In the Environment Variables window (pictured below), highlight the Path variable in the System variables section and click the Edit button. Add or modify the path lines with the paths you want the computer to access. Each different directory is separated with a semicolon, as shown below:

C:\Program Files;C:\Winnt;C:\Winnt\System32

The first time I searched for it, it immediately popped up the System Properties Window. After that, I found the above instructions.

Colspan all columns

For IE 6, you'll want to equal colspan to the number of columns in your table. If you have 5 columns, then you'll want: colspan="5".

The reason is that IE handles colspans differently, it uses the HTML 3.2 specification:

IE implements the HTML 3.2 definition, it sets colspan=0 as colspan=1.

The bug is well documented.

How often should Oracle database statistics be run?

At my last job we ran statistics once a week. If I remember correctly, we scheduled them on a Thursday night, and on Friday the DBAs were very careful to monitor the longest running queries for anything unexpected. (Friday was picked because it was often just after a code release, and tended to be a fairly low traffic day.) When they saw a bad query they would find a better query plan and save that one so it wouldn't change again unexpectedly. (Oracle has tools to do this for you automatically, you tell it the query to optimize and it does.)

Many organizations avoid running statistics out of fear of bad query plans popping up unexpectedly. But this usually means that their query plans get worse and worse over time. And when they do run statistics then they encounter a number of problems. The resulting scramble to fix those issues confirms their fears about the dangers of running statistics. But if they ran statistics regularly, used the monitoring tools as they are supposed to, and fixed issues as they came up then they would have fewer headaches, and they wouldn't encounter them all at once.

How does a PreparedStatement avoid or prevent SQL injection?

To understand how PreparedStatement prevents SQL Injection, we need to understand phases of SQL Query execution.

1. Compilation Phase. 2. Execution Phase.

Whenever SQL server engine receives a query, it has to pass through below phases,

Query Execution Phases

  1. Parsing and Normalization Phase: In this phase, Query is checked for syntax and semantics. It checks whether references table and columns used in query exist or not. It also has many other tasks to do, but let's not go in detail.

  2. Compilation Phase: In this phase, keywords used in query like select, from, where etc are converted into format understandable by machine. This is the phase where query is interpreted and corresponding action to be taken is decided. It also has many other tasks to do, but let's not go in detail.

  3. Query Optimization Plan: In this phase, Decision Tree is created for finding the ways in which query can be executed. It finds out the number of ways in which query can be executed and the cost associated with each way of executing Query. It chooses the best plan for executing a query.

  4. Cache: Best plan selected in Query optimization plan is stored in cache, so that whenever next time same query comes in, it doesn't have to pass through Phase 1, Phase 2 and Phase 3 again. When next time query come in, it will be checked directly in Cache and picked up from there to execute.

  5. Execution Phase: In this phase, supplied query gets executed and data is returned to user as ResultSet object.

Behaviour of PreparedStatement API on above steps

  1. PreparedStatements are not complete SQL queries and contain placeholder(s), which at run time are replaced by actual user-provided data.

  2. Whenever any PreparedStatment containing placeholders is passed in to SQL Server engine, It passes through below phases

    1. Parsing and Normalization Phase
    2. Compilation Phase
    3. Query Optimization Plan
    4. Cache (Compiled Query with placeholders are stored in Cache.)

UPDATE user set username=? and password=? WHERE id=?

  1. Above query will get parsed, compiled with placeholders as special treatment, optimized and get Cached. Query at this stage is already compiled and converted in machine understandable format. So we can say that Query stored in cache is Pre-Compiled and only placeholders need to be replaced with user-provided data.

  2. Now at run-time when user-provided data comes in, Pre-Compiled Query is picked up from Cache and placeholders are replaced with user-provided data.

PrepareStatementWorking

(Remember, after place holders are replaced with user data, final query is not compiled/interpreted again and SQL Server engine treats user data as pure data and not a SQL that needs to be parsed or compiled again; that is the beauty of PreparedStatement.)

If the query doesn't have to go through compilation phase again, then whatever data replaced on the placeholders are treated as pure data and has no meaning to SQL Server engine and it directly executes the query.

Note: It is the compilation phase after parsing phase, that understands/interprets the query structure and gives meaningful behavior to it. In case of PreparedStatement, query is compiled only once and cached compiled query is picked up all the time to replace user data and execute.

Due to one time compilation feature of PreparedStatement, it is free of SQL Injection attack.

You can get detailed explanation with example here: https://javabypatel.blogspot.com/2015/09/how-prepared-statement-in-java-prevents-sql-injection.html

Convert String to double in Java

double d = Double.parseDouble(aString);

This should convert the string aString into the double d.

Difference between DOM parentNode and parentElement

there is one more difference, but only in internet explorer. It occurs when you mix HTML and SVG. if the parent is the 'other' of those two, then .parentNode gives the parent, while .parentElement gives undefined.

how to write javascript code inside php

You can put up all your JS like this, so it doesn't execute before your HTML is ready

$(document).ready(function() {
   // some code here
 });

Remember this is jQuery so include it in the head section. Also see Why you should use jQuery and not onload

What's the difference between process.cwd() vs __dirname?

Knowing the scope of each can make things easier to remember.

process is node's global object, and .cwd() returns where node is running.

__dirname is module's property, and represents the file path of the module. In node, one module resides in one file.

Similarly, __filename is another module's property, which holds the file name of the module.

How to turn off the Eclipse code formatter for certain sections of Java code?

If you put the plus sign on the beginning of the line, it formats differently:

String query = 
    "SELECT FOO, BAR, BAZ" 
    +    "  FROM ABC"           
    +    " WHERE BAR > 4";

What is a wrapper class?

A wrapper class is a class that serves the sole purpose of holding something and adding some functionality to it. In Java since the primitives (like ints,floats,chars...) are not objects so if you want to treat them like one then you have to use a wrapper class. Suppose you want to create a Vector of ints, the problem is a Vector only holds Objects not primitives. So what you will do is put all the ints in an Integer wrapper and use that. Example:

int number = 5;
Integer numberWrapped = new Integer(number);
//now you have the int in an object.
//and this is how to access the int value that is being wrapped.
int again = numberWrapped.intValue();

How to print to the console in Android Studio?

You can see the println() statements in the Run window of Android Studio.

See detailed answer with screenshot here.

VirtualBox error "Failed to open a session for the virtual machine"

try this

sudo update-secureboot-policy --enroll-key

and restart your system, when restart it shows option and select Mok key and you will work fine.

C++ Array of pointers: delete or delete []?

It would make sens if your code was like this:

#include <iostream>

using namespace std;

class Monster
{
public:
        Monster() { cout << "Monster!" << endl; }
        virtual ~Monster() { cout << "Monster Died" << endl; }
};

int main(int argc, const char* argv[])
{
        Monster *mon = new Monster[6];

        delete [] mon;

        return 0;
}

How to read a specific line using the specific line number from a file in Java?

Use this code:

import java.nio.file.Files;

import java.nio.file.Paths;

public class FileWork 
{

    public static void main(String[] args) throws IOException {

        String line = Files.readAllLines(Paths.get("D:/abc.txt")).get(1);

        System.out.println(line);  
    }

}

Detect if a page has a vertical scrollbar?

I wrote an updated version of Kees C. Bakker's answer:

const hasVerticalScroll = (node) => {
  if (!node) {
    if (window.innerHeight) {
      return document.body.offsetHeight > window.innerHeight
    }
    return (document.documentElement.scrollHeight > document.documentElement.offsetHeight)
      || (document.body.scrollHeight > document.body.offsetHeight)
  }
  return node.scrollHeight > node.offsetHeight
}

if (hasVerticalScroll(document.querySelector('body'))) {
  this.props.handleDisableDownScrollerButton()
}

The function returns true or false depending whether the page has a vertical scrollbar or not.

For example:

const hasVScroll = hasVerticalScroll(document.querySelector('body'))

if (hasVScroll) {
  console.log('HAS SCROLL', hasVScroll)
}

Creating a BAT file for python script

If this is a BAT file in a different directory than the current directory, you may see an error like "python: can't open file 'somescript.py': [Errno 2] No such file or directory". This can be fixed by specifying an absolute path to the BAT file using %~dp0 (the drive letter and path of that batch file).

@echo off
python %~dp0\somescript.py %*

(This way you can ignore the c:\ or whatever, because perhaps you may want to move this script)

Uploading Images to Server android

Try this method for uploading Image file from camera

package com.example.imageupload;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.http.Header;
import org.apache.http.HttpEntity;
import org.apache.http.message.BasicHeader;

public class MultipartEntity implements HttpEntity {

private String boundary = null;

ByteArrayOutputStream out = new ByteArrayOutputStream();
boolean isSetLast = false;
boolean isSetFirst = false;

public MultipartEntity() {
    this.boundary = System.currentTimeMillis() + "";
}

public void writeFirstBoundaryIfNeeds() {
    if (!isSetFirst) {
        try {
            out.write(("--" + boundary + "\r\n").getBytes());
        } catch (final IOException e) {

        }
    }
    isSetFirst = true;
}

public void writeLastBoundaryIfNeeds() {
    if (isSetLast) {
        return;
    }
    try {
        out.write(("\r\n--" + boundary + "--\r\n").getBytes());
    } catch (final IOException e) {

    }
    isSetLast = true;
}

public void addPart(final String key, final String value) {
    writeFirstBoundaryIfNeeds();
    try {
        out.write(("Content-Disposition: form-data; name=\"" + key + "\"\r\n")
                .getBytes());
        out.write("Content-Type: text/plain; charset=UTF-8\r\n".getBytes());
        out.write("Content-Transfer-Encoding: 8bit\r\n\r\n".getBytes());
        out.write(value.getBytes());
        out.write(("\r\n--" + boundary + "\r\n").getBytes());
    } catch (final IOException e) {

    }
}

public void addPart(final String key, final String fileName,
        final InputStream fin) {
    addPart(key, fileName, fin, "application/octet-stream");
}

public void addPart(final String key, final String fileName,
        final InputStream fin, String type) {
    writeFirstBoundaryIfNeeds();
    try {
        type = "Content-Type: " + type + "\r\n";
        out.write(("Content-Disposition: form-data; name=\"" + key
                + "\"; filename=\"" + fileName + "\"\r\n").getBytes());
        out.write(type.getBytes());
        out.write("Content-Transfer-Encoding: binary\r\n\r\n".getBytes());

        final byte[] tmp = new byte[4096];
        int l = 0;
        while ((l = fin.read(tmp)) != -1) {
            out.write(tmp, 0, l);
        }
        out.flush();
    } catch (final IOException e) {

    } finally {
        try {
            fin.close();
        } catch (final IOException e) {

        }
    }
}

public void addPart(final String key, final File value) {
    try {
        addPart(key, value.getName(), new FileInputStream(value));
    } catch (final FileNotFoundException e) {

    }
}

public long getContentLength() {
    writeLastBoundaryIfNeeds();
    return out.toByteArray().length;
}

public Header getContentType() {
    return new BasicHeader("Content-Type", "multipart/form-data; boundary="
            + boundary);
}

public boolean isChunked() {
    return false;
}

public boolean isRepeatable() {
    return false;
}

public boolean isStreaming() {
    return false;
}

public void writeTo(final OutputStream outstream) throws IOException {
    outstream.write(out.toByteArray());
}

public Header getContentEncoding() {
    return null;
}

public void consumeContent() throws IOException,
        UnsupportedOperationException {
    if (isStreaming()) {
        throw new UnsupportedOperationException(
                "Streaming entity does not implement #consumeContent()");
    }
}

public InputStream getContent() throws IOException,
        UnsupportedOperationException {
    return new ByteArrayInputStream(out.toByteArray());
}

}

Use of class for uploading

private void doFileUpload(File file_path) {

    Log.d("Uri", "Do file path" + file_path);

    try {

        HttpClient client = new DefaultHttpClient();
        //use your server path of php file
        HttpPost post = new HttpPost(ServerUploadPath);

        Log.d("ServerPath", "Path" + ServerUploadPath);

        FileBody bin1 = new FileBody(file_path);
        Log.d("Enter", "Filebody complete " + bin1);

        MultipartEntity reqEntity = new MultipartEntity();
        reqEntity.addPart("uploaded_file", bin1);
        reqEntity.addPart("email", new StringBody(useremail));

        post.setEntity(reqEntity);
        Log.d("Enter", "Image send complete");

        HttpResponse response = client.execute(post);
        resEntity = response.getEntity();
        Log.d("Enter", "Get Response");
        try {

            final String response_str = EntityUtils.toString(resEntity);
            if (resEntity != null) {
                Log.i("RESPONSE", response_str);
                JSONObject jobj = new JSONObject(response_str);
                result = jobj.getString("ResponseCode");
                Log.e("Result", "...." + result);

            }
        } catch (Exception ex) {
            Log.e("Debug", "error: " + ex.getMessage(), ex);
        }
    } catch (Exception e) {
        Log.e("Upload Exception", "");
        e.printStackTrace();
    }
}

Service for uploading

   <?php
$image_name = $_FILES["uploaded_file"]["name"]; 
$tmp_arr = explode(".",$image_name);
$img_extn = end($tmp_arr);
$new_image_name = 'image_'. uniqid() .'.'.$img_extn;    
$flag=0;                 

if (file_exists("Images/".$new_image_name))
{
           $msg=$new_image_name . " already exists."
           header('Content-type: application/json');        
           echo json_encode(array("ResponseCode"=>"2","ResponseMsg"=>$msg));        
}else{  
move_uploaded_file($_FILES["uploaded_file"]["tmp_name"],"Images/". $new_image_name);
                   $flag = 1;
}   

if($flag == 1){                    
            require 'db.php';   
            $static_url =$new_image_name;
            $conn=mysql_connect($db_host,$db_username,$db_password) or die("unable to connect localhost".mysql_error());
            $db=mysql_select_db($db_database,$conn) or die("unable to select message_app"); 
            $email = "";
            if((isset($_REQUEST['email'])))
            {
                     $email = $_REQUEST['email'];
            }

    $sql ="insert into alert(images) values('$static_url')";

     $result=mysql_query($sql);

     if($result){
    echo json_encode(array("ResponseCode"=>"1","ResponseMsg"=> "Insert data successfully.","Result"=>"True","ImageName"=>$static_url,"email"=>$email));
       } else
       {

         echo json_encode(array("ResponseCode"=>"2","ResponseMsg"=> "Could not insert data.","Result"=>"False","email"=>$email));
        }
}
    else{
    echo json_encode(array("ResponseCode"=>"2","ResponseMsg"=> "Erroe While Inserting Image.","Result"=>"False"));
    }
    ?>

How to resolve "could not execute statement; SQL [n/a]; constraint [numbering];"?

In my case, I had a OneToOne relation which I was using with @Column by mistake. I changed it to @JoinColumn and added @OneToOne annotation and it fixed the exception.

window.open(url, '_blank'); not working on iMac/Safari

Safari is blocking any call to window.open() which is made inside an async call.

The solution that I found to this problem is to call window.open before making an asnyc call and set the location when the promise resolves.

var windowReference = window.open();

myService.getUrl().then(function(url) {
     windowReference.location = url;
});

compare differences between two tables in mysql

Based on Haim's answer here's a simplified example if you're looking to compare values that exist in BOTH tables, otherwise if there's a row in one table but not the other it will also return it....

Took me a couple of hours to figure out. Here's a fully tested simply query for comparing "tbl_a" and "tbl_b"

SELECT ID, col
FROM
(
    SELECT
    tbl_a.ID, tbl_a.col FROM tbl_a
    UNION ALL
    SELECT
    tbl_b.ID, tbl_b.col FROM tbl_b
) t
WHERE ID IN (select ID from tbl_a) AND ID IN (select ID from tbl_b)
GROUP BY
ID, col
HAVING COUNT(*) = 1
 ORDER BY ID

So you need to add the extra "where in" clause:

WHERE ID IN (select ID from tbl_a) AND ID IN (select ID from tbl_b)


Also:

For ease of reading if you want to indicate the table names you can use the following:

SELECT tbl, ID, col
FROM
(
    SELECT
    tbl_a.ID, tbl_a.col, "name_to_display1" as "tbl" FROM tbl_a
    UNION ALL
    SELECT
    tbl_b.ID, tbl_b.col, "name_to_display2" as "tbl" FROM tbl_b
) t
WHERE ID IN (select ID from tbl_a) AND ID IN (select ID from tbl_b)
GROUP BY
ID, col
HAVING COUNT(*) = 1
 ORDER BY ID

YYYY-MM-DD format date in shell script

In bash (>=4.2) it is preferable to use printf's built-in date formatter (part of bash) rather than the external date (usually GNU date).

As such:

# put current date as yyyy-mm-dd in $date
# -1 -> explicit current date, bash >=4.3 defaults to current time if not provided
# -2 -> start time for shell
printf -v date '%(%Y-%m-%d)T\n' -1 

# put current date as yyyy-mm-dd HH:MM:SS in $date
printf -v date '%(%Y-%m-%d %H:%M:%S)T\n' -1 

# to print directly remove -v flag, as such:
printf '%(%Y-%m-%d)T\n' -1
# -> current date printed to terminal

In bash (<4.2):

# put current date as yyyy-mm-dd in $date
date=$(date '+%Y-%m-%d')

# put current date as yyyy-mm-dd HH:MM:SS in $date
date=$(date '+%Y-%m-%d %H:%M:%S')

# print current date directly
echo $(date '+%Y-%m-%d')

Other available date formats can be viewed from the date man pages (for external non-bash specific command):

man date

Scroll to a div using jquery

OK guys, this is a small solution, but it works fine.

suppose the following code:

<div id='the_div_holder' style='height: 400px; overflow-y: scroll'>
  <div class='post'>1st post</div>
  <div class='post'>2nd post</div>
  <div class='post'>3rd post</div>
</div>

you want when a new post is added to 'the_div_holder' then it scrolls its inner content (the div's .post) to the last one like a chat. So, do the following whenever a new .post is added to the main div holder:

var scroll = function(div) {
    var totalHeight = 0;
    div.find('.post').each(function(){
       totalHeight += $(this).outerHeight();
    });
    div.scrollTop(totalHeight);
  }
  // call it:
  scroll($('#the_div_holder'));

How to reload the current route with the angular 2 router

As far as I know this can't be done with the router in Angular 2. But you could just do:

window.location.href = window.location.href

To reload the view.

Specify multiple attribute selectors in CSS

Concatenate the attribute selectors:

input[name="Sex"][value="M"]

Eclipse can't find / load main class

I solved my issue by doing this:

  • cut the entire main (CTRL X) out of the class (just for a few seconds),
  • save the class file (CTRL S)
  • paste the main back exactly at the same place (CTRL V)

Strangely it started working again after that.

INSERT statement conflicted with the FOREIGN KEY constraint - SQL Server

Parent table data missing causes the problem. In your problem non availability of data in "dbo.Sup_Item_Cat" causes the problem

HTML anchor link - href and onclick both?

<a href="#Foo" onclick="return runMyFunction();">Do it!</a>

and

function runMyFunction() {
  //code
  return true;
}

This way you will have youf function executed AND you will follow the link AND you will follow the link exactly after your function was successfully run.

application/x-www-form-urlencoded or multipart/form-data?

I agree with much that Manuel has said. In fact, his comments refer to this url...

http://www.w3.org/TR/html401/interact/forms.html#h-17.13.4

... which states:

The content type "application/x-www-form-urlencoded" is inefficient for sending large quantities of binary data or text containing non-ASCII characters. The content type "multipart/form-data" should be used for submitting forms that contain files, non-ASCII data, and binary data.

However, for me it would come down to tool/framework support.

  • What tools and frameworks do you expect your API users to be building their apps with?
  • Do they have frameworks or components they can use that favour one method over the other?

If you get a clear idea of your users, and how they'll make use of your API, then that will help you decide. If you make the upload of files hard for your API users then they'll move away, of you'll spend a lot of time on supporting them.

Secondary to this would be the tool support YOU have for writing your API and how easy it is for your to accommodate one upload mechanism over the other.

CSS table td width - fixed, not flexible

Just divide the number of td to 100%. Example, you have 4 td's:

<html>
<table>
<tr>
<td style="width:25%">This is a text</td>
<td style="width:25%">This is some text, this is some text</td>
<td style="width:25%">This is another text, this is another text</td>
<td style="width:25%">This is the last text, this is the last text</td>
</tr>
</table>
</html>

We use 25% in each td to maximize the 100% space of the entire table

Nested JSON objects - do I have to use arrays for everything?

You have too many redundant nested arrays inside your jSON data, but it is possible to retrieve the information. Though like others have said you might want to clean it up.

use each() wrap within another each() until the last array.

for result.data[0].stuff[0].onetype[0] in jQuery you could do the following:

`

$.each(data.result.data, function(index0, v) {
    $.each(v, function (index1, w) {
        $.each(w, function (index2, x) {
            alert(x.id);
        });
    });

});

`

Pandas df.to_csv("file.csv" encode="utf-8") still gives trash characters for minus sign

Your "bad" output is UTF-8 displayed as CP1252.

On Windows, many editors assume the default ANSI encoding (CP1252 on US Windows) instead of UTF-8 if there is no byte order mark (BOM) character at the start of the file. While a BOM is meaningless to the UTF-8 encoding, its UTF-8-encoded presence serves as a signature for some programs. For example, Microsoft Office's Excel requires it even on non-Windows OSes. Try:

df.to_csv('file.csv',encoding='utf-8-sig')

That encoder will add the BOM.

How to get form input array into PHP array

What if you've got array of fieldsets?

<fieldset>
<input type="text" name="item[1]" />
<input type="text" name="item[2]" />
<input type="hidden" name="fset[]"/>
</fieldset>

<fieldset>
<input type="text" name="item[3]" />
<input type="text" name="item[4]" />
<input type="hidden" name="fset[]"/>
</fieldset>

I added a hidden field to count the number of the fieldsets. The user can add or delete the fields and then save it.

How to define hash tables in Bash?

There's parameter substitution, though it may be un-PC as well ...like indirection.

#!/bin/bash

# Array pretending to be a Pythonic dictionary
ARRAY=( "cow:moo"
        "dinosaur:roar"
        "bird:chirp"
        "bash:rock" )

for animal in "${ARRAY[@]}" ; do
    KEY="${animal%%:*}"
    VALUE="${animal##*:}"
    printf "%s likes to %s.\n" "$KEY" "$VALUE"
done

printf "%s is an extinct animal which likes to %s\n" "${ARRAY[1]%%:*}" "${ARRAY[1]##*:}"

The BASH 4 way is better of course, but if you need a hack ...only a hack will do. You could search the array/hash with similar techniques.

Using getResources() in non-activity class

here is my answer:

public class WigetControl {
private Resources res;

public WigetControl(Resources res) 
{
    this.res = res;
}

public void setButtonDisable(Button mButton)
{
    mButton.setBackgroundColor(res.getColor(R.color.loginbutton_unclickable));
    mButton.setEnabled(false);
}

}

and the call can be like this:

        WigetControl control = new WigetControl(getResources());
        control.setButtonDisable(btNext);

How to convert byte array to string

Assuming that you are using UTF-8 encoding:

string convert = "This is the string to be converted";

// From string to byte array
byte[] buffer = System.Text.Encoding.UTF8.GetBytes(convert);

// From byte array to string
string s = System.Text.Encoding.UTF8.GetString(buffer, 0, buffer.Length);

java Arrays.sort 2d array

much simpler code:

import java.util.Arrays; int[][] array = new int[][];

Arrays.sort(array, ( a, b) -> a[1] - b[1]);

bootstrap 3 wrap text content within div for horizontal alignment

Now Update word-wrap is replace by :

overflow-wrap:break-word;

Compatible old navigator and css 3 it's good alternative !

it's evolution of word-wrap ( since 2012... )

See more information : https://www.w3.org/TR/css-text-3/#overflow-wrap

See compatibility full : http://caniuse.com/#search=overflow-wrap

Use formula in custom calculated field in Pivot Table

I'll post this comment as answer, as I'm confident enough that what I asked is not possible.

I) Couple of similar questions trying to do the same, without success:

II) This article: Excel Pivot Table Calculated Field for example lists many restrictions of Calculated Field:

  • For calculated fields, the individual amounts in the other fields are summed, and then the calculation is performed on the total amount.
  • Calculated field formulas cannot refer to the pivot table totals or subtotals
  • Calculated field formulas cannot refer to worksheet cells by address or by name.
  • Sum is the only function available for a calculated field.
  • Calculated fields are not available in an OLAP-based pivot table.

III) There is tiny limited possibility to use AVERAGE() and similar function for a range of cells, but that applies only if Pivot table doesn't have grouped cells, which allows listing the cells as items in new group (right to "Fileds" listbox in above screenshot) and then user can calculate AVERAGE(), referencing explicitly every item (cell), from Items listbox, as argument. Maybe it's better explained here: Calculate values in a PivotTable report
For my Pivot table it wasn't applicable because my range wasn't small enough, this option to be sane choice.

Serializing/deserializing with memory stream

This code works for me:

public void Run()
{
    Dog myDog = new Dog();
    myDog.Name= "Foo";
    myDog.Color = DogColor.Brown;

    System.Console.WriteLine("{0}", myDog.ToString());

    MemoryStream stream = SerializeToStream(myDog);

    Dog newDog = (Dog)DeserializeFromStream(stream);

    System.Console.WriteLine("{0}", newDog.ToString());
}

Where the types are like this:

[Serializable]
public enum DogColor
{
    Brown,
    Black,
    Mottled
}

[Serializable]
public class Dog
{
    public String Name
    {
        get; set;
    }

    public DogColor Color
    {
        get;set;
    }

    public override String ToString()
    {
        return String.Format("Dog: {0}/{1}", Name, Color);
    }
}

and the utility methods are:

public static MemoryStream SerializeToStream(object o)
{
    MemoryStream stream = new MemoryStream();
    IFormatter formatter = new BinaryFormatter();
    formatter.Serialize(stream, o);
    return stream;
}

public static object DeserializeFromStream(MemoryStream stream)
{
    IFormatter formatter = new BinaryFormatter();
    stream.Seek(0, SeekOrigin.Begin);
    object o = formatter.Deserialize(stream);
    return o;
}

Hide div if screen is smaller than a certain width

I have the almost the same situation as yours; that if the screen width is less than the my specified width it should hide the div. This is the jquery code I used that worked for me.

$(window).resize(function() {

  if ($(this).width() < 1024) {

    $('.divIWantedToHide').hide();

  } else {

    $('.divIWantedToHide').show();

    }

});

Error:Execution failed for task ':app:transformClassesWithDexForDebug' in android studio

i have tried this one and it worked for me. hope it works for others too.

  1. Open build.gradle module file
  2. downgrade you sdkversion from 25 to 24 or 23
  3. add 'multiDexEnabled true'
  4. comment this line : compile 'com.android.support:appcompat-v7:25.1.0' (if it's in 'dependencies')
  5. Sync your project and ready to go.

Here i have attached screenshot to explain things. Go through this steps

happy to help.

thanks.

Merge 2 DataTables and store in a new one

This is what i did for merging two datatables and bind the final result to the gridview

        DataTable dtTemp=new DataTable();
        for (int k = 0; k < GridView2.Rows.Count; k++)
        {
            string roomno = GridView2.Rows[k].Cells[1].Text;
            DataTable dtx = GetRoomDetails(chk, roomno, out msg);
            if (dtx.Rows.Count > 0)
            {
                dtTemp.Merge(dtx);
                dtTemp.AcceptChanges();

            }
        }

How can I scroll a div to be visible in ReactJS?

Another example which uses function in ref rather than string

class List extends React.Component {
  constructor(props) {
    super(props);
    this.state = { items:[], index: 0 };
    this._nodes = new Map();

    this.handleAdd = this.handleAdd.bind(this);
    this.handleRemove = this.handleRemove.bind(this);
   }

  handleAdd() {
    let startNumber = 0;
    if (this.state.items.length) {
      startNumber = this.state.items[this.state.items.length - 1];
    }

    let newItems = this.state.items.splice(0);
    for (let i = startNumber; i < startNumber + 100; i++) {
      newItems.push(i);
    }

    this.setState({ items: newItems });
  }

  handleRemove() {
    this.setState({ items: this.state.items.slice(1) });
  }

  handleShow(i) {
    this.setState({index: i});
    const node = this._nodes.get(i);
    console.log(this._nodes);
    if (node) {
      ReactDOM.findDOMNode(node).scrollIntoView({block: 'end', behavior: 'smooth'});
    }
  }

  render() {
    return(
      <div>
        <ul>{this.state.items.map((item, i) => (<Item key={i} ref={(element) => this._nodes.set(i, element)}>{item}</Item>))}</ul>
        <button onClick={this.handleShow.bind(this, 0)}>0</button>
        <button onClick={this.handleShow.bind(this, 50)}>50</button>
        <button onClick={this.handleShow.bind(this, 99)}>99</button>
        <button onClick={this.handleAdd}>Add</button>
        <button onClick={this.handleRemove}>Remove</button>
        {this.state.index}
      </div>
    );
  }
}

class Item extends React.Component
{
  render() {
    return (<li ref={ element => this.listItem = element }>
      {this.props.children}
    </li>);
  }
}

Demo: https://codepen.io/anon/pen/XpqJVe

Python SQL query string formatting

Cleanest way I have come across is inspired by the sql style guide.

sql = """
    SELECT field1, field2, field3, field4
      FROM table
     WHERE condition1 = 1
       AND condition2 = 2;
"""

Essentially, the keywords that begin a clause should be right-aligned and the field names etc, should be left aligned. This looks very neat and is easier to debug as well.

How to install/start Postman native v4.10.3 on Ubuntu 16.04 LTS 64-bit?

Was having an issue getting the "Run in Postman" links to work with the browsers until I added this to the .desktop file

MimeType=application/postman;x-scheme-handler/postman;

What is the main purpose of setTag() getTag() methods of View?

This is very useful for custom ArrayAdapter using. It is some kind of optimization. There setTag used as reference to object that references on some parts of layout (that displaying in ListView) instead of findViewById.

static class ViewHolder {
    TextView tvPost;
    TextView tvDate;
    ImageView thumb;
}

public View getView(int position, View convertView, ViewGroup parent) {

    if (convertView == null) {
        LayoutInflater inflater = myContext.getLayoutInflater();
        convertView = inflater.inflate(R.layout.postitem, null);

        ViewHolder vh = new ViewHolder();
        vh.tvPost = (TextView)convertView.findViewById(R.id.postTitleLabel);
        vh.tvDate = (TextView)convertView.findViewById(R.id.postDateLabel);
        vh.thumb = (ImageView)convertView.findViewById(R.id.postThumb);
        convertView.setTag(vh);
    }
            ....................
}

How to set String's font size, style in Java using the Font class?

Font myFont = new Font("Serif", Font.BOLD, 12);, then use a setFont method on your components like

JButton b = new JButton("Hello World");
b.setFont(myFont);

How can I hide or encrypt JavaScript code?

You can obfuscate it, but there's no way of protecting it completely.

example obfuscator: https://obfuscator.io

how to disable DIV element and everything inside

I think inline scripts are hard to stop instead you can try with this:

<div id="test">
    <div>Click Me</div>
</div>

and script:

$(function () {
    $('#test').children().click(function(){
      alert('hello');
    });
    $('#test').children().off('click');
});

CHEKOUT FIDDLE AND SEE IT HELPS

Read More about .off()

Difference between a Structure and a Union

With a union, you're only supposed to use one of the elements, because they're all stored at the same spot. This makes it useful when you want to store something that could be one of several types. A struct, on the other hand, has a separate memory location for each of its elements and they all can be used at once.

To give a concrete example of their use, I was working on a Scheme interpreter a little while ago and I was essentially overlaying the Scheme data types onto the C data types. This involved storing in a struct an enum indicating the type of value and a union to store that value.

union foo {
  int a;   // can't use both a and b at once
  char b;
} foo;

struct bar {
  int a;   // can use both a and b simultaneously
  char b;
} bar;

union foo x;
x.a = 3; // OK
x.b = 'c'; // NO! this affects the value of x.a!

struct bar y;
y.a = 3; // OK
y.b = 'c'; // OK

edit: If you're wondering what setting x.b to 'c' changes the value of x.a to, technically speaking it's undefined. On most modern machines a char is 1 byte and an int is 4 bytes, so giving x.b the value 'c' also gives the first byte of x.a that same value:

union foo x;
x.a = 3;
x.b = 'c';
printf("%i, %i\n", x.a, x.b);

prints

99, 99

Why are the two values the same? Because the last 3 bytes of the int 3 are all zero, so it's also read as 99. If we put in a larger number for x.a, you'll see that this is not always the case:

union foo x;
x.a = 387439;
x.b = 'c';
printf("%i, %i\n", x.a, x.b);

prints

387427, 99

To get a closer look at the actual memory values, let's set and print out the values in hex:

union foo x;
x.a = 0xDEADBEEF;
x.b = 0x22;
printf("%x, %x\n", x.a, x.b);

prints

deadbe22, 22

You can clearly see where the 0x22 overwrote the 0xEF.

BUT

In C, the order of bytes in an int are not defined. This program overwrote the 0xEF with 0x22 on my Mac, but there are other platforms where it would overwrite the 0xDE instead because the order of the bytes that make up the int were reversed. Therefore, when writing a program, you should never rely on the behavior of overwriting specific data in a union because it's not portable.

For more reading on the ordering of bytes, check out endianness.

Define an alias in fish shell

Save your files as ~/.config/fish/functions/{some_function_name}.fish and they should get autoloaded when you start fish.

Converting Pandas dataframe into Spark dataframe error

You need to make sure your pandas dataframe columns are appropriate for the type spark is inferring. If your pandas dataframe lists something like:

pd.info()
<class 'pandas.core.frame.DataFrame'>
RangeIndex: 5062 entries, 0 to 5061
Data columns (total 51 columns):
SomeCol                    5062 non-null object
Col2                       5062 non-null object

And you're getting that error try:

df[['SomeCol', 'Col2']] = df[['SomeCol', 'Col2']].astype(str)

Now, make sure .astype(str) is actually the type you want those columns to be. Basically, when the underlying Java code tries to infer the type from an object in python it uses some observations and makes a guess, if that guess doesn't apply to all the data in the column(s) it's trying to convert from pandas to spark it will fail.

How can I make my layout scroll both horizontally and vertically?

I was able to find a simple way to achieve both scrolling behaviors.

Here is the xml for it:

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent" android:layout_height="fill_parent"
    android:scrollbars="vertical">

    <HorizontalScrollView 
        android:layout_width="320px" android:layout_height="fill_parent">

        <TableLayout
            android:id="@+id/linlay" android:layout_width="320px"
            android:layout_height="fill_parent" android:stretchColumns="1"
            android:background="#000000"/>

    </HorizontalScrollView>

</ScrollView>

Message Queue vs. Web Services?

Message queues are asynchronous and can retry a number of times if delivery fails. Use a message queue if the requester doesn't need to wait for a response.

The phrase "web services" make me think of synchronous calls to a distributed component over HTTP. Use web services if the requester needs a response back.

How to pass a URI to an intent?

The Uri class implements Parcelable, so you can add and extract it directly from the Intent

// Add a Uri instance to an Intent
intent.putExtra("imageUri", uri);

// Get a Uri from an Intent
Uri uri = intent.getParcelableExtra("imageUri");

You can use the same method for any objects that implement Parcelable, and you can implement Parcelable on your own objects if required.

How to replace spaces in file names using a bash script

you can use detox by Doug Harple

detox -r <folder>

Running JAR file on Windows 10

How do I run an executable JAR file? If you have a jar file called Example.jar, follow these rules:

Open a notepad.exe.
Write : java -jar Example.jar.
Save it with the extension .bat.
Copy it to the directory which has the .jar file.
Double click it to run your .jar file.

In Node.js, how do I turn a string to a json?

You need to use this function.

JSON.parse(yourJsonString);

And it will return the object / array that was contained within the string.

allowing only alphabets in text box using java script

You can use HTML5 pattern attribute to do this:

<form>
    <input type='text' pattern='[A-Za-z\\s]*'/>
</form>

If the user enters an input that conflicts with the pattern, it will show an error dialogue automatically.

Do C# Timers elapse on a separate thread?

It depends. The System.Timers.Timer has two modes of operation.

If SynchronizingObject is set to an ISynchronizeInvoke instance then the Elapsed event will execute on the thread hosting the synchronizing object. Usually these ISynchronizeInvoke instances are none other than plain old Control and Form instances that we are all familiar with. So in that case the Elapsed event is invoked on the UI thread and it behaves similar to the System.Windows.Forms.Timer. Otherwise, it really depends on the specific ISynchronizeInvoke instance that was used.

If SynchronizingObject is null then the Elapsed event is invoked on a ThreadPool thread and it behaves similar to the System.Threading.Timer. In fact, it actually uses a System.Threading.Timer behind the scenes and does the marshaling operation after it receives the timer callback if needed.

What is the difference between .yaml and .yml extension?

As @David Heffeman indicates the recommendation is to use .yaml when possible, and the recommendation has been that way since September 2006.

That some projects use .yml is mostly because of ignorance of the implementers/documenters: they wanted to use YAML because of readability, or some other feature not available in other formats, were not familiar with the recommendation and and just implemented what worked, maybe after looking at some other project/library (without questioning whether what was done is correct).

The best way to approach this is to be rigorous when creating new files (i.e. use .yaml) and be permissive when accepting input (i.e. allow .yml when you encounter it), possible automatically upgrading/correcting these errors when possible.

The other recommendation I have is to document the argument(s) why you have to use .yml, when you think you have to. That way you don't look like an ignoramus, and give others the opportunity to understand your reasoning. Of course "everybody else is doing it" and "On Google .yml has more pages than .yaml" are not arguments, they are just statistics about the popularity of project(s) that have it wrong or right (with regards to the extension of YAML files). You can try to prove that some projects are popular, just because they use a .yml extension instead of the correct .yaml, but I think you will be hard pressed to do so.

Some projects realize (too late) that they use the incorrect extension (e.g. originally docker-compose used .yml, but in later versions started to use .yaml, although they still support .yml). Others still seem ignorant about the correct extension, like AppVeyor early 2019, but allow you to specify the configuration file for a project, including extension. This allows you to get the configuration file out of your face as well as giving it the proper extension: I use .appveyor.yaml instead of appveyor.yml for building the windows wheels of my YAML parser for Python).


On the other hand:

The Yaml (sic!) component of Symfony2 implements a selected subset of features defined in the YAML 1.2 version specification.

So it seems fitting that they also use a subset of the recommended extension.

What does the clearfix class do in css?

When an element, such as a div is floated, its parent container no longer considers its height, i.e.

<div id="main">
  <div id="child" style="float:left;height:40px;"> Hi</div>
</div>

The parent container will not be be 40 pixels tall by default. This causes a lot of weird little quirks if you're using these containers to structure layout.

So the clearfix class that various frameworks use fixes this problem by making the parent container "acknowledge" the contained elements.

Day to day, I normally just use frameworks such as 960gs, Twitter Bootstrap for laying out and not bothering with the exact mechanics.

Can read more here

http://www.webtoolkit.info/css-clearfix.html

How do I get today's date in C# in mm/dd/yyyy format?

string today = DateTime.Today.ToString("M/d");

How to make an Asynchronous Method return a value?

You should use the EndXXX of your async method to return the value. EndXXX should wait until there is a result using the IAsyncResult's WaitHandle and than return with the value.

Spring 3 MVC resources and tag <mvc:resources />

As said by @Nancom

<mvc:resources location="/resources/" mapping="/resource/**"/>

So for clarity lets our image is in

resources/images/logo.png"

The location attribute of the mvc:resources tag defines the base directory location of static resources that you want to serve. It can be images path that are available under the src/main/webapp/resources/images/ directory; you may wonder why we have given only /resources/ as the location value instead of src/main/webapp/resources/images/. This is because we consider the resources directory as the base directory for all resources, we can have multiple sub-directories under resources directory to put our images and other static resource files.

The second attribute, mapping, just indicates the request path that needs to be mapped to this resources directory. In our case, we have assigned /resource/** as the mapping value. So, if any web request starts with the /resource request path, then it will be mapped to the resources directory, and the /** symbol indicates the recursive look for any resource files underneath the base resources directory.

So for url like http://localhost:8080/webstore/resource/images/logo.png. So, while serving this web request, Spring MVC will consider /resource/images/logo.png as the request path. So, it will try to map /resource to the base directory specified by the location attribute, resources. From this directory, it will try to look for the remaining path of the URL, which is /images/logo.png. Since we have the images directory under the resources directory, Spring can easily locate the image file from the images directory.

So

 <mvc:resources location="/resources/" mapping="/resource/**"/>

gives us for given [requests] -> [resource mapping]:

http://localhost:8080/webstore/resource/images/logo.png -> searches in resources/images/logo.png

http://localhost:8080/webstore/resource/images/small/picture.png -> searches in resources/images/small/picture.png

http://localhost:8080/webstore/resource/css/main.css -> searches in resources/css/main.css

http://localhost:8080/webstore/resource/pdf/index.pdf -> searches in resources/pdf/index.pdf

In an array of objects, fastest way to find the index of an object whose attributes match a search

As I can't comment yet, I want to show the solution I used based on the method Umair Ahmed posted, but when you want to search for a key instead of a value:

[{"a":true}, {"f":true}, {"g":false}]
.findIndex(function(element){return Object.keys(element)[0] == "g"});

I understand that it doesn't answer the expanded question, but the title doesn't specify what was wanted from each object, so I want to humbly share this to save headaches to others in the future, while I undestart it may not be the fastest solution.

MySQL select all rows from last month until (now() - 1 month), for comparative purposes

maybe like this - all last month DATE(recDate) BETWEEN DATE_ADD(LAST_DAY(DATE_SUB(CURDATE(), INTERVAL 2 MONTH)), INTERVAL 1 DAY) AND LAST_DAY(DATE_SUB(CURDATE(), INTERVAL 1 MONTH) )

Artisan migrate could not find driver

if you've installed php and mysql in your linux machine, php needs php-mysql extention to communicate with mysql. so make sure you've also installed this extention using:

sudo yum install php-mysql in redhat based machines.

and

sudo apt-get install php-mysql in debian machines.

How do I wait for a promise to finish before returning the variable of a function?

What do I need to do to make this function wait for the result of the promise?

Use async/await (NOT Part of ECMA6, but available for Chrome, Edge, Firefox and Safari since end of 2017, see canIuse)
MDN

    async function waitForPromise() {
        // let result = await any Promise, like:
        let result = await Promise.resolve('this is a sample promise');
    }

Added due to comment: An async function always returns a Promise, and in TypeScript it would look like:

    async function waitForPromise(): Promise<string> {
        // let result = await any Promise, like:
        let result = await Promise.resolve('this is a sample promise');
    }

Getting an "ambiguous redirect" error

I've recently found that blanks in the name of the redirect file will cause the "ambiguous redirect" message.

For example if you redirect to application$(date +%Y%m%d%k%M%S).log and you specify the wrong formatting characters, the redirect will fail before 10 AM for example. If however, you used application$(date +%Y%m%d%H%M%S).log it would succeed. This is because the %k format yields ' 9' for 9AM where %H yields '09' for 9AM.

echo $(date +%Y%m%d%k%M%S) gives 20140626 95138

echo $(date +%Y%m%d%H%M%S) gives 20140626095138

The erroneous date might give something like:

echo "a" > myapp20140626 95138.log

where the following is what would be desired:

echo "a" > myapp20140626095138.log

Show loading gif after clicking form submit using jQuery

The show() method only affects the display CSS setting. If you want to set the visibility you need to do it directly. Also, the .load_button element is a button and does not raise a submit event. You would need to change your selector to the form for that to work:

$('#login_form').submit(function() {
    $('#gif').css('visibility', 'visible');
});

Also note that return true; is redundant in your logic, so it can be removed.

How to set max and min value for Y axis

Just set the value for scaleStartValue in your options.

var options = {
   // ....
   scaleStartValue: 0,
}

See the documentation for this here.

Android Studio: Module won't show up in "Edit Configuration"

I managed to fix it in Android Studio 1.3.1 by doing the following:

  1. Make a new module from File -> New -> New Module
  2. Name it something different, e.g. 'My Libary'
  3. Copy an .iml file from an existing library module and change the name of the file and rename references in the .iml file
  4. Add the module name to settings.gradle
  5. Add the module dependency in your app's build.gradle file 'compile project(':mylibrary')'
  6. Close and reopen Android Studio
  7. Verify that Android Studio recognises the module as a library (should be bold)
  8. Rename module's directory and module name by right clicking on the newly created module.
  9. Enjoy :)

How do I check if file exists in Makefile so I can delete it?

It's strange to see so many people using shell scripting for this. I was looking for a way to use native makefile syntax, because I'm writing this outside of any target. You can use the wildcard function to check if file exists:

 ifeq ($(UNAME),Darwin)
     SHELL := /opt/local/bin/bash
     OS_X  := true
 else ifneq (,$(wildcard /etc/redhat-release))
     OS_RHEL := true
 else
     OS_DEB  := true
     SHELL := /bin/bash
 endif 

Update:

I found a way which is really working for me:

ifneq ("$(wildcard $(PATH_TO_FILE))","")
    FILE_EXISTS = 1
else
    FILE_EXISTS = 0
endif

Python reshape list to ndim array

The answers above are good. Adding a case that I used. Just if you don't want to use numpy and keep it as list without changing the contents.

You can run a small loop and change the dimension from 1xN to Nx1.

    tmp=[]
    for b in bus:
        tmp.append([b])
    bus=tmp

It is maybe not efficient while in case of very large numbers. But it works for a small set of numbers. Thanks

Any way to return PHP `json_encode` with encode UTF-8 and not Unicode?

Use JSON_UNESCAPED_UNICODE inside json_encode() if your php version >=5.4.

Improve subplot size/spacing with many subplots in matplotlib

You can use plt.subplots_adjust to change the spacing between the subplots (source)

call signature:

subplots_adjust(left=None, bottom=None, right=None, top=None, wspace=None, hspace=None)

The parameter meanings (and suggested defaults) are:

left  = 0.125  # the left side of the subplots of the figure
right = 0.9    # the right side of the subplots of the figure
bottom = 0.1   # the bottom of the subplots of the figure
top = 0.9      # the top of the subplots of the figure
wspace = 0.2   # the amount of width reserved for blank space between subplots
hspace = 0.2   # the amount of height reserved for white space between subplots

The actual defaults are controlled by the rc file

How to sum the values of a JavaScript object?

If you're using lodash you can do something like

_.sum(_.values({ 'a': 1 , 'b': 2 , 'c':3 })) 

Display a table/list data dynamically in MVC3/Razor from a JsonResult?

As Mystere Man suggested, getting just a view first and then again making an ajax call again to get the json result is unnecessary in this case. that is 2 calls to the server. I think you can directly return an HTML table of Users in the first call.

We will do this in this way. We will have a strongly typed view which will return the markup of list of users to the browser and this data is being supplied by an action method which we will invoke from our browser using an http request.

Have a ViewModel for the User

public class UserViewModel
{
  public int UserID { set;get;}
  public string FirstName { set;get;}
   //add remaining properties as per your requirement

}

and in your controller have a method to get a list of Users

public class UserController : Controller
{

   [HttpGet]
   public ActionResult List()
   {
     List<UserViewModel> objList=UserService.GetUsers();  // this method should returns list of  Users
     return View("users",objList)        
   }
}

Assuming that UserService.GetUsers() method will return a List of UserViewModel object which represents the list of usres in your datasource (Tables)

and in your users.cshtml ( which is under Views/User folder),

 @model List<UserViewModel>

 <table>

 @foreach(UserViewModel objUser in Model)
 {
   <tr>
      <td>@objUser.UserId.ToString()</td>
      <td>@objUser.FirstName</td>
   </tr>
 }
 </table>

All Set now you can access the url like yourdomain/User/List and it will give you a list of users in an HTML table.

What is the HTML tabindex attribute?

tabindex is a global attribute responsible for two things:

  1. it sets the order of "focusable" elements and
  2. it makes elements "focusable".

In my mind the second thing is even more important than the first one. There are very few elements that are focusable by default (e.g. <a> and form controls). Developers very often add some JavaScript event handlers (like 'onclick') on not focusable elements (<div>, <span> and so on), and the way to make your interface be responsive not only to mouse events but also to keyboard events (e.g. 'onkeypress') is to make such elements focusable. Lastly, if you don't want to set the order but just make your element focusable use tabindex="0" on all such elements:

<div tabindex="0"></div>

Also, if you don't want it to be focusable via the tab key then use tabindex="-1". For example, the below link will not be focused while using tab keys to traverse.

<a href="#" tabindex="-1">Tab key cannot reach here!</a>

How to return a dictionary | Python

I followed approach as shown in code below to return a dictionary. Created a class and declared dictionary as global and created a function to add value corresponding to some keys in dictionary.

**Note have used Python 2.7 so some minor modification might be required for Python 3+

class a:
    global d
    d={}
    def get_config(self,x):
        if x=='GENESYS':
            d['host'] = 'host name'
            d['port'] = '15222'
        return d

Calling get_config method using class instance in a separate python file:

from constant import a
class b:
    a().get_config('GENESYS')
    print a().get_config('GENESYS').get('host')
    print a().get_config('GENESYS').get('port')

CREATE TABLE LIKE A1 as A2

Based on http://dev.mysql.com/doc/refman/5.0/en/create-table-select.html

What about:

Create Table New_Users Select * from Old_Users Where 1=2;

and if that doesn't work, just select a row and truncate after creation:

Create table New_Users select * from Old_Users Limit 1;
Truncate Table New_Users;

EDIT:

I noticed your comment below about needing indexes, etc. Try:

show create table old_users;
#copy the output ddl statement into a text editor and change the table name to new_users
#run the new query
insert into new_users(id,name...) select id,name,... form old_users group by id;

That should do it. It appears that you are doing this to get rid of duplicates? In which case you may want to put a unique index on id. if it's a primary key, this should already be in place. You can either:

#make primary key
alter table new_users add primary key (id);
#make unique
create unique index idx_new_users_id_uniq on new_users (id);

Inserting values into a SQL Server database using ado.net via C#

private void button1_Click(object sender, EventArgs e)
{
    SqlConnection con = new SqlConnection();
    con.ConnectionString = "data source=CHANCHAL\SQLEXPRESS;initial catalog=AssetManager;user id=GIPL-PC\GIPL;password=";
    con.Open();
    SqlDataAdapter ad = new SqlDataAdapter("select * from detail1", con);
    SqlCommandBuilder cmdbl = new SqlCommandBuilder(ad);
    DataSet ds = new DataSet("detail1");
    ad.Fill(ds, "detail1");
    DataRow row = ds.Tables["detail1"].NewRow();
    row["Name"] = textBox1.Text;
    row["address"] =textBox2.Text;
    ds.Tables["detail1"].Rows.Add(row);
    ad.Update(ds, "detail1");
    con.Close();
    MessageBox.Show("insert secussfully"); 
}

How to export plots from matplotlib with transparent background?

Use the matplotlib savefig function with the keyword argument transparent=True to save the image as a png file.

In [30]: x = np.linspace(0,6,31)

In [31]: y = np.exp(-0.5*x) * np.sin(x)

In [32]: plot(x, y, 'bo-')
Out[32]: [<matplotlib.lines.Line2D at 0x3f29750>]            

In [33]: savefig('demo.png', transparent=True)

Result: demo.png

Of course, that plot doesn't demonstrate the transparency. Here's a screenshot of the PNG file displayed using the ImageMagick display command. The checkerboard pattern is the background that is visible through the transparent parts of the PNG file.

display screenshot

Sending mail from Python using SMTP

Or

import smtplib
 
from email.message import EmailMessage
from getpass import getpass


password = getpass()

message = EmailMessage()
message.set_content('Message content here')
message['Subject'] = 'Your subject here'
message['From'] = "USERNAME@DOMAIN"
message['To'] = "[email protected]"

try:
    smtp_server = None
    smtp_server = smtplib.SMTP("YOUR.MAIL.SERVER", 587)
    smtp_server.ehlo()
    smtp_server.starttls()
    smtp_server.ehlo()
    smtp_server.login("USERNAME@DOMAIN", password)
    smtp_server.send_message(message)
except Exception as e:
    print("Error: ", str(e))
finally:
    if smtp_server is not None:
        smtp_server.quit()

If you want to use Port 465 you have to create an SMTP_SSL object.

How can I get the intersection, union, and subset of arrays in Ruby?

Utilizing the fact that you can do set operations on arrays by doing &(intersection), -(difference), and |(union).

Obviously I didn't implement the MultiSet to spec, but this should get you started:

class MultiSet
  attr_accessor :set
  def initialize(set)
    @set = set
  end
  # intersection
  def &(other)
    @set & other.set
  end
  # difference
  def -(other)
    @set - other.set
  end
  # union
  def |(other)
    @set | other.set
  end
end

x = MultiSet.new([1,1,2,2,3,4,5,6])
y = MultiSet.new([1,3,5,6])

p x - y # [2,2,4]
p x & y # [1,3,5,6]
p x | y # [1,2,3,4,5,6]

select the TOP N rows from a table

select * from table_name LIMIT 100

remember this only works with MYSQL

sort dict by value python

In your comment in response to John, you suggest that you want the keys and values of the dictionary, not just the values.

PEP 256 suggests this for sorting a dictionary by values.

import operator
sorted(d.iteritems(), key=operator.itemgetter(1))

If you want descending order, do this

sorted(d.iteritems(), key=itemgetter(1), reverse=True)

How do I convert certain columns of a data frame to become factors?

Given the following sample

myData <- data.frame(A=rep(1:2, 3), B=rep(1:3, 2), Pulse=20:25)  

then

myData$A <-as.factor(myData$A)
myData$B <-as.factor(myData$B)

or you could select your columns altogether and wrap it up nicely:

# select columns
cols <- c("A", "B")
myData[,cols] <- data.frame(apply(myData[cols], 2, as.factor))

levels(myData$A) <- c("long", "short")
levels(myData$B) <- c("1kg", "2kg", "3kg")

To obtain

> myData
      A   B Pulse
1  long 1kg    20
2 short 2kg    21
3  long 3kg    22
4 short 1kg    23
5  long 2kg    24
6 short 3kg    25

Slide div left/right using jQuery

$('#hello').hide('slide', {direction: 'left'}, 1000); requires the jQuery-ui library. See http://www.jqueryui.com

Resizing an image in an HTML5 canvas

I have a feeling the module I wrote will produce similar results to photoshop, as it preserves color data by averaging them, not applying an algorithm. It's kind of slow, but to me it is the best, because it preserves all the color data.

https://github.com/danschumann/limby-resize/blob/master/lib/canvas_resize.js

It doesn't take the nearest neighbor and drop other pixels, or sample a group and take a random average. It takes the exact proportion each source pixel should output into the destination pixel. The average pixel color in the source will be the average pixel color in the destination, which these other formulas, I think they will not be.

an example of how to use is at the bottom of https://github.com/danschumann/limby-resize

UPDATE OCT 2018: These days my example is more academic than anything else. Webgl is pretty much 100%, so you'd be better off resizing with that to produce similar results, but faster. PICA.js does this, I believe. –

Is there an XSL "contains" directive?

From Zvon.org XSLT Reference:

XPath function: boolean contains (string, string) 

Hope this helps.

What is the proper way to comment functions in Python?

Read about using docstrings in your Python code.

As per the Python docstring conventions:

The docstring for a function or method should summarize its behavior and document its arguments, return value(s), side effects, exceptions raised, and restrictions on when it can be called (all if applicable). Optional arguments should be indicated. It should be documented whether keyword arguments are part of the interface.

There will be no golden rule, but rather provide comments that mean something to the other developers on your team (if you have one) or even to yourself when you come back to it six months down the road.

How to increase Java heap space for a tomcat app

Just set this extra line in catalina.bat file

LINE NO AROUND: 143

set "CATALINA_OPTS=-Xms512m -Xmx512m"

And restart Tomcat service

Ansible: get current target host's IP address

If you want the external public IP and you're in a cloud environment like AWS or Azure, you can use the ipify_facts module:

# TODO: SECURITY: This requires that we trust ipify to provide the correct public IP. We could run our own ipify server.
- name: Get my public IP from ipify.org
  ipify_facts:

This will place the public IP into the variable ipify_public_ip.