I've got a list of People that are returned from an external app and I'm creating an exclusion list in my local app to give me the option of manually removing people from the list.
I have a composite key which I have created that is common to both and I want to find an efficient way of removing people from my List using my List
e.g
class Person
{
prop string compositeKey { get; set; }
}
class Exclusions
{
prop string compositeKey { get; set; }
}
List<Person> people = GetFromDB;
List<Exclusions> exclusions = GetFromOtherDB;
List<Person> filteredResults = People - exclustions using the composite key as a comparer
I thought LINQ was the ideal way of doing this but after trying joins, extension methods, using yields, etc. I'm still having trouble.
If this were SQL I would use a not in (?,?,?) query.
This question is related to
c#
linq
list
linq-to-objects
Have a look at the Except method, which you use like this:
var resultingList =
listOfOriginalItems.Except(listOfItemsToLeaveOut, equalityComparer)
You'll want to use the overload I've linked to, which lets you specify a custom IEqualityComparer. That way you can specify how items match based on your composite key. (If you've already overridden Equals, though, you shouldn't need the IEqualityComparer.)
Edit: Since it appears you're using two different types of classes, here's another way that might be simpler. Assuming a List<Person> called persons and a List<Exclusion> called exclusions:
var exclusionKeys =
exclusions.Select(x => x.compositeKey);
var resultingPersons =
persons.Where(x => !exclusionKeys.Contains(x.compositeKey));
In other words: Select from exclusions just the keys, then pick from persons all the Person objects that don't have any of those keys.
I would do something like this but i bet there is a simpler way. i think the sql from linqtosql would use a select from person Where NOT EXIST(select from your exclusion list)
static class Program
{
public class Person
{
public string Key { get; set; }
public Person(string key)
{
Key = key;
}
}
public class NotPerson
{
public string Key { get; set; }
public NotPerson(string key)
{
Key = key;
}
}
static void Main()
{
List<Person> persons = new List<Person>()
{
new Person ("1"),
new Person ("2"),
new Person ("3"),
new Person ("4")
};
List<NotPerson> notpersons = new List<NotPerson>()
{
new NotPerson ("3"),
new NotPerson ("4")
};
var filteredResults = from n in persons
where !notpersons.Any(y => n.Key == y.Key)
select n;
foreach (var item in filteredResults)
{
Console.WriteLine(item.Key);
}
}
}
This LINQ below will generate the SQL for a left outer join and then take all of the results that don't find a match in your exclusion list.
List<Person> filteredResults =from p in people
join e in exclusions on p.compositeKey equals e.compositeKey into temp
from t in temp.DefaultIfEmpty()
where t.compositeKey == null
select p
let me know if it works!
Many thanks for this guys.
I mangaged to get this down to one line:
var results = from p in People
where !(from e in exclusions
select e.CompositeKey).Contains(p.CompositeKey)
select p;
Thanks again everyone.
You can use the "Except" extension method (see http://msdn.microsoft.com/en-us/library/bb337804.aspx)
In your code
var difference = people.Except(exclusions);
I would just use the FindAll method on the List class. i.e.:
List<Person> filteredResults =
people.FindAll(p => return !exclusions.Contains(p));
Not sure if the syntax will exactly match your objects, but I think you can see where I'm going with this.
Many thanks for this guys.
I mangaged to get this down to one line:
var results = from p in People
where !(from e in exclusions
select e.CompositeKey).Contains(p.CompositeKey)
select p;
Thanks again everyone.
I would just use the FindAll method on the List class. i.e.:
List<Person> filteredResults =
people.FindAll(p => return !exclusions.Contains(p));
Not sure if the syntax will exactly match your objects, but I think you can see where I'm going with this.
I would do something like this but i bet there is a simpler way. i think the sql from linqtosql would use a select from person Where NOT EXIST(select from your exclusion list)
static class Program
{
public class Person
{
public string Key { get; set; }
public Person(string key)
{
Key = key;
}
}
public class NotPerson
{
public string Key { get; set; }
public NotPerson(string key)
{
Key = key;
}
}
static void Main()
{
List<Person> persons = new List<Person>()
{
new Person ("1"),
new Person ("2"),
new Person ("3"),
new Person ("4")
};
List<NotPerson> notpersons = new List<NotPerson>()
{
new NotPerson ("3"),
new NotPerson ("4")
};
var filteredResults = from n in persons
where !notpersons.Any(y => n.Key == y.Key)
select n;
foreach (var item in filteredResults)
{
Console.WriteLine(item.Key);
}
}
}
var thisList = new List<string>{ "a", "b", "c" };
var otherList = new List<string> {"a", "b"};
var theOnesThatDontMatch = thisList
.Where(item=> otherList.All(otherItem=> item != otherItem))
.ToList();
var theOnesThatDoMatch = thisList
.Where(item=> otherList.Any(otherItem=> item == otherItem))
.ToList();
Console.WriteLine("don't match: {0}", string.Join(",", theOnesThatDontMatch));
Console.WriteLine("do match: {0}", string.Join(",", theOnesThatDoMatch));
//Output:
//don't match: c
//do match: a,b
Adapt the list types and lambdas accordingly, and you can filter out anything.
var result = Data.Where(x =>
{
bool condition = true;
double accord = (double)x[Table.Columns.IndexOf(FiltercomboBox.Text)];
return condition && accord >= double.Parse(FilterLowertextBox.Text) && accord <= double.Parse(FilterUppertextBox.Text);
});
I couldn't figure out how to do this in pure MS LINQ, so I wrote my own extension method to do it:
public static bool In<T>(this T objToCheck, params T[] values)
{
if (values == null || values.Length == 0)
{
return false; //early out
}
else
{
foreach (T t in values)
{
if (t.Equals(objToCheck))
return true; //RETURN found!
}
return false; //nothing found
}
}
This LINQ below will generate the SQL for a left outer join and then take all of the results that don't find a match in your exclusion list.
List<Person> filteredResults =from p in people
join e in exclusions on p.compositeKey equals e.compositeKey into temp
from t in temp.DefaultIfEmpty()
where t.compositeKey == null
select p
let me know if it works!
I would just use the FindAll method on the List class. i.e.:
List<Person> filteredResults =
people.FindAll(p => return !exclusions.Contains(p));
Not sure if the syntax will exactly match your objects, but I think you can see where I'm going with this.
This LINQ below will generate the SQL for a left outer join and then take all of the results that don't find a match in your exclusion list.
List<Person> filteredResults =from p in people
join e in exclusions on p.compositeKey equals e.compositeKey into temp
from t in temp.DefaultIfEmpty()
where t.compositeKey == null
select p
let me know if it works!
var thisList = new List<string>{ "a", "b", "c" };
var otherList = new List<string> {"a", "b"};
var theOnesThatDontMatch = thisList
.Where(item=> otherList.All(otherItem=> item != otherItem))
.ToList();
var theOnesThatDoMatch = thisList
.Where(item=> otherList.Any(otherItem=> item == otherItem))
.ToList();
Console.WriteLine("don't match: {0}", string.Join(",", theOnesThatDontMatch));
Console.WriteLine("do match: {0}", string.Join(",", theOnesThatDoMatch));
//Output:
//don't match: c
//do match: a,b
Adapt the list types and lambdas accordingly, and you can filter out anything.
I couldn't figure out how to do this in pure MS LINQ, so I wrote my own extension method to do it:
public static bool In<T>(this T objToCheck, params T[] values)
{
if (values == null || values.Length == 0)
{
return false; //early out
}
else
{
foreach (T t in values)
{
if (t.Equals(objToCheck))
return true; //RETURN found!
}
return false; //nothing found
}
}
var result = Data.Where(x =>
{
bool condition = true;
double accord = (double)x[Table.Columns.IndexOf(FiltercomboBox.Text)];
return condition && accord >= double.Parse(FilterLowertextBox.Text) && accord <= double.Parse(FilterUppertextBox.Text);
});
You can use the "Except" extension method (see http://msdn.microsoft.com/en-us/library/bb337804.aspx)
In your code
var difference = people.Except(exclusions);
I couldn't figure out how to do this in pure MS LINQ, so I wrote my own extension method to do it:
public static bool In<T>(this T objToCheck, params T[] values)
{
if (values == null || values.Length == 0)
{
return false; //early out
}
else
{
foreach (T t in values)
{
if (t.Equals(objToCheck))
return true; //RETURN found!
}
return false; //nothing found
}
}
I would just use the FindAll method on the List class. i.e.:
List<Person> filteredResults =
people.FindAll(p => return !exclusions.Contains(p));
Not sure if the syntax will exactly match your objects, but I think you can see where I'm going with this.
This LINQ below will generate the SQL for a left outer join and then take all of the results that don't find a match in your exclusion list.
List<Person> filteredResults =from p in people
join e in exclusions on p.compositeKey equals e.compositeKey into temp
from t in temp.DefaultIfEmpty()
where t.compositeKey == null
select p
let me know if it works!
I would do something like this but i bet there is a simpler way. i think the sql from linqtosql would use a select from person Where NOT EXIST(select from your exclusion list)
static class Program
{
public class Person
{
public string Key { get; set; }
public Person(string key)
{
Key = key;
}
}
public class NotPerson
{
public string Key { get; set; }
public NotPerson(string key)
{
Key = key;
}
}
static void Main()
{
List<Person> persons = new List<Person>()
{
new Person ("1"),
new Person ("2"),
new Person ("3"),
new Person ("4")
};
List<NotPerson> notpersons = new List<NotPerson>()
{
new NotPerson ("3"),
new NotPerson ("4")
};
var filteredResults = from n in persons
where !notpersons.Any(y => n.Key == y.Key)
select n;
foreach (var item in filteredResults)
{
Console.WriteLine(item.Key);
}
}
}
Many thanks for this guys.
I mangaged to get this down to one line:
var results = from p in People
where !(from e in exclusions
select e.CompositeKey).Contains(p.CompositeKey)
select p;
Thanks again everyone.
I couldn't figure out how to do this in pure MS LINQ, so I wrote my own extension method to do it:
public static bool In<T>(this T objToCheck, params T[] values)
{
if (values == null || values.Length == 0)
{
return false; //early out
}
else
{
foreach (T t in values)
{
if (t.Equals(objToCheck))
return true; //RETURN found!
}
return false; //nothing found
}
}
You can use the "Except" extension method (see http://msdn.microsoft.com/en-us/library/bb337804.aspx)
In your code
var difference = people.Except(exclusions);
I would do something like this but i bet there is a simpler way. i think the sql from linqtosql would use a select from person Where NOT EXIST(select from your exclusion list)
static class Program
{
public class Person
{
public string Key { get; set; }
public Person(string key)
{
Key = key;
}
}
public class NotPerson
{
public string Key { get; set; }
public NotPerson(string key)
{
Key = key;
}
}
static void Main()
{
List<Person> persons = new List<Person>()
{
new Person ("1"),
new Person ("2"),
new Person ("3"),
new Person ("4")
};
List<NotPerson> notpersons = new List<NotPerson>()
{
new NotPerson ("3"),
new NotPerson ("4")
};
var filteredResults = from n in persons
where !notpersons.Any(y => n.Key == y.Key)
select n;
foreach (var item in filteredResults)
{
Console.WriteLine(item.Key);
}
}
}
You can use the "Except" extension method (see http://msdn.microsoft.com/en-us/library/bb337804.aspx)
In your code
var difference = people.Except(exclusions);
Source: Stackoverflow.com