How to do associative array hashing in JavaScript

Question

I need to store some statistics using JavaScript in a way like I d do it in C      Dictionary lt string  int gt  statistics   statistics  Foo     10  statistics  Goo     statistics  Goo     1  statistics Add  Zoo   1     Is there an Hashtable or something like Dictionary lt TKey  TValue gt  in JavaScript  How could I store values in such a way

User · Answer

All modern browsers support a JavaScript Map object. There are a couple of reasons that make using a Map better than Object:

An Object has a prototype, so there are default keys in the map.

The keys of an Object are Strings, where they can be any value for a Map.

You can get the size of a Map easily while you have to keep track of size for an Object.

Example:

var myMap = new Map();

var keyObj = {},
    keyFunc = function () {},
    keyString = "a string";

myMap.set(keyString, "value associated with 'a string'");
myMap.set(keyObj, "value associated with keyObj");
myMap.set(keyFunc, "value associated with keyFunc");

myMap.size; // 3

myMap.get(keyString);    // "value associated with 'a string'"
myMap.get(keyObj);       // "value associated with keyObj"
myMap.get(keyFunc);      // "value associated with keyFunc"

If you want keys that are not referenced from other objects to be garbage collected, consider using a WeakMap instead of a Map.

User · Answer

In C  the code looks like  Dictionary lt string int gt  dictionary   new Dictionary lt string int gt     dictionary add  quot sample1 quot   1   dictionary add  quot sample2 quot   2    or var dictionary   new Dictionary lt string  int gt          quot sample1 quot   1         quot sample2 quot   2      In JavaScript  var dictionary          quot sample1 quot   1       quot sample2 quot   2    A C  dictionary object contains useful methods  like dictionary ContainsKey   In JavaScript  we could use the hasOwnProperty like  if  dictionary hasOwnProperty  quot sample1 quot        console log  quot sample1 key found and its value is quot   dictionary  quot sample1 quot

User · Answer

Use JavaScript objects as associative arrays   Associative Array  In simple words associative arrays use Strings instead of Integer numbers as index   Create an object with var dictionary         JavaScript allows you to add properties to objects by using the following syntax   Object yourProperty   value   An alternate syntax for the same is  Object  quot yourProperty quot     value   If you can  also create key-to-value object maps with the following syntax  var point     x 3  y 2     point  quot x quot      returns 3 point y    returns 2   You can iterate through an associative array using the for  in loop construct as follows  for var key in Object keys dict      var value   dict key        use key value for intended purpose

User · Answer

Years ago  I implemented the following hashtable  which has had some features that have been missing to the Map class  However  that s no longer the case  Now it s possible to iterate over the entries of a Map  get an array of its keys or values or both  these operations are implemented copying to a newly allocated array  though     that s a waste of memory and its time complexity will always be as bad as O n    remove specific items given their key  and clear the whole map  Therefore  my hashtable implementation is only useful for compatibility purposes  though in this case it would be more appropriate to write a proper polyfill  I d suggest to anyone who would use my hashtable implementation to change it so to make it become a polyfill for the Map class  function Hashtable         this  map   new Map        this  indexes   new Map        this  keys           this  values           this put   function key  value            var newKey    this containsKey key           this  map set key  value           if  newKey                this  indexes set key  this length               this  keys push key               this  values push value                        this remove   function key            if   this containsKey key               return          this  map delete key           var index   this  indexes get key           this  indexes delete key           this  keys splice index  1           this  values splice index  1              this indexOfKey   function key            return this  indexes get key              this indexOfValue   function value            return this  values indexOf value     -1             this get   function key            return this  map get key              this entryAt   function index            var item               Object defineProperty item   quot key quot                 value  this keys index               writable  false                     Object defineProperty item   quot value quot                 value  this values index               writable  false                     return item             this clear   function             var length   this length          for  var i   0  i  lt  length  i                  var key   this keys i               this  map delete key               this  indexes delete key                     this  keys splice 0  length              this containsKey   function key            return this  map has key              this containsValue   function value            return this  values indexOf value     -1             this forEach   function iterator            for  var i   0  i  lt  this length  i                iterator this keys i   this values i   i              Object defineProperty this   quot length quot             get  function                 return this  keys length                        Object defineProperty this   quot keys quot             get  function                 return this  keys                        Object defineProperty this   quot values quot             get  function                 return this  values                        Object defineProperty this   quot entries quot             get  function                 var entries   new Array this length               for  var i   0  i  lt  entries length  i                    entries i    this entryAt i               return entries                       Documentation of the class Hashtable Methods   get key  Returns the value associated to the specified key  Parameters  key  The key from which to retrieve the value   put key  value  Associates the specified value to the specified key  Parameters  key  The key to which associate the value  value  The value to associate to the key   remove key  Removes the specified key  together with the value associated to it  Parameters  key  The key to remove   clear   Clears the whole hashtable  by removing all its entries   indexOfKey key  Returns the index of the specified key  according to the order entries have been added  Parameters  key  The key of which to get the index   indexOfValue value  Returns the index of the specified value  according to the order entries have been added  Parameters  value  The value of which to get the index  Remarks  This information is retrieved using the indexOf   method of an array  so objects are compared by identity   entryAt index  Returns an object with a key and a value properties  representing the entry at the specified index  Parameters  index  The index of the entry to get   containsKey key  Returns whether the hashtable contains the specified key  Parameters  key  The key to look for   containsValue value  Returns whether the hashtable contains the specified value  Parameters  value  The value to look for   forEach iterator  Iterates through all the entries in the hashtable  calling specified iterator  Parameters  iterator  A method with three parameters  key  value and index  where index represents the index of the entry according to the order it s been added    Properties   length  Read-only  Gets the count of the entries in the hashtable   keys  Read-only  Gets an array of all the keys in the hashtable   values  Read-only  Gets an array of all the values in the hashtable   entries  Read-only  Gets an array of all the entries in the hashtable  They re represented the same as the method entryAt   does

User · Answer

function HashTable         this length   0      this items   new Array        for  var i   0  i  lt  arguments length  i    2            if  typeof  arguments i   1       undefined                 this items arguments i     arguments i   1               this length                         this removeItem   function  in key            var tmp previous          if  typeof  this items in key       undefined                 this length--              var tmp previous   this items in key               delete this items in key                      return tmp previous             this getItem   function  in key            return this items in key              this setItem   function  in key  in value            var tmp previous          if  typeof  in value      undefined                 if  typeof  this items in key       undefined                     this length                  else                   tmp previous   this items in key                              this items in key    in value                     return tmp previous             this hasItem   function  in key            return typeof  this items in key       undefined              this clear   function              for  var i in this items                delete this items i                      this length   0

User · Answer

If you require your keys to be any object rather than just strings  then you could use my jshashtable

User · Answer

Unless you have a specific reason not to  just use a normal object  Object properties in JavaScript can be referenced using hashtable-style syntax  var hashtable       hashtable foo    quot bar quot   hashtable  bar      quot foo quot    Both foo and bar elements can now then be referenced as  hashtable  foo    hashtable  bar        Or hashtable foo  hashtable bar   Of course this does mean your keys have to be strings  If they re not strings they are converted internally to strings  so it may still work  Your mileage may vary

User · Answer

Since every object in JavaScript behaves like - and is generally implemented as - a hashtable  I just go with that    var hashSweetHashTable

User · Answer

var associativeArray       associativeArray  one      First   associativeArray  two      Second   associativeArray  three      Third     If you are coming from an object-oriented language you should check this article

User · Answer

https   gist github com alexhawkins f6329420f40e5cafa0a4 var HashTable   function       this  storage         this  count   0    this  limit   8      HashTable prototype insert   function key  value          Create an index for our storage location by passing      it through our hashing function   var index   this hashFunc key  this  limit         Retrieve the bucket at this particular index in      our storage  if one exists         k v    k v    k v         k v    k v        k v        var bucket   this  storage index        Does a bucket exist or do we get undefined      when trying to retrieve said index    if   bucket           Create the bucket     var bucket              Insert the bucket into our hashTable     this  storage index    bucket         var override   false        Now iterate through our bucket to see if there are any conflicting      key value pairs within our bucket  If there are any  override them    for  var i   0  i  lt  bucket length  i          var tuple   bucket i       if  tuple 0      key              Override value stored at this key       tuple 1    value        override   true               if   override           Create a new tuple in our bucket         Note that this could either be the new empty bucket we created above        or a bucket with other tupules with keys that are different than        the key of the tuple we are inserting  These tupules are in the same        bucket because their keys all equate to the same numeric index when        passing through our hash function      bucket push  key  value        this  count           Now that we ve added our new key val pair to our storage        let s check to see if we need to resize our storage     if  this  count  gt  this  limit   0 75          this resize this  limit   2               return this       HashTable prototype remove   function key      var index   this hashFunc key  this  limit     var bucket   this  storage index     if   bucket        return null            Iterate over the bucket   for  var i   0  i  lt  bucket length  i          var tuple   bucket i           Check to see if key is inside bucket     if  tuple 0      key              If it is  get rid of this tuple       bucket splice i  1         this  count--        if  this  count  lt  this  limit   0 25            this  resize this  limit   2                 return tuple 1                  HashTable prototype retrieve   function key      var index   this hashFunc key  this  limit     var bucket   this  storage index      if   bucket        return null         for  var i   0  i  lt  bucket length  i          var tuple   bucket i       if  tuple 0      key          return tuple 1                return null       HashTable prototype hashFunc   function str  max      var hash   0    for  var i   0  i  lt  str length  i          var letter   str i       hash    hash  lt  lt  5    letter charCodeAt 0       hash    hash  amp  hash    max        return hash       HashTable prototype resize   function newLimit      var oldStorage   this  storage     this  limit   newLimit    this  count   0    this  storage          oldStorage forEach function bucket        if   bucket          return            for  var i   0  i  lt  bucket length  i            var tuple   bucket i         this insert tuple 0   tuple 1              bind this         HashTable prototype retrieveAll   function       console log this  storage       console log this  limit                                      TESTS                                  var hashT   new HashTable     hashT insert  Alex Hawkins    510-599-1930      hashT retrieve                   Alex Hawkins    510-599-1930        hashT insert  Boo Radley    520-589-1970      hashT retrieve               Boo Radley    520-589-1970              Alex Hawkins    510-599-1930        hashT insert  Vance Carter    120-589-1970   insert  Rick Mires    520-589-1970   insert  Tom Bradey    520-589-1970   insert  Biff Tanin    520-589-1970      hashT retrieveAll                  Boo Radley    520-589-1970            Tom Bradey    520-589-1970                  Alex Hawkins    510-599-1930            Rick Mires    520-589-1970                      Biff Tanin    520-589-1970               Override example  Phone Number Change     hashT insert  Rick Mires    650-589-1970   insert  Tom Bradey    818-589-1970   insert  Biff Tanin    987-589-1970      hashT retrieveAll                   Boo Radley    520-589-1970            Tom Bradey    818-589-1970                  Alex Hawkins    510-599-1930            Rick Mires    650-589-1970                      Biff Tanin    987-589-1970             hashT remove  Rick Mires    hashT remove  Tom Bradey      hashT retrieveAll                   Boo Radley    520-589-1970                  Alex Hawkins    510-599-1930                      Biff Tanin    987-589-1970              hashT insert  Dick Mires    650-589-1970   insert  Lam James    818-589-1970   insert  Ricky Ticky Tavi    987-589-1970    hashT retrieveAll         NOTICE HOW THE HASH TABLE HAS NOW DOUBLED IN SIZE UPON REACHING 75  CAPACITY  i e  6 8  It is now size 16                 Vance Carter    120-589-1970              Alex Hawkins    510-599-1930            Dick Mires    650-589-1970            Lam James    818-589-1970                                  Boo Radley    520-589-1970            Ricky Ticky Tavi    987-589-1970                              Biff Tanin    987-589-1970             console log hashT retrieve  Lam James         818-589-1970 console log hashT retrieve  Dick Mires        650-589-1970 console log hashT retrieve  Ricky Ticky Tavi       987-589-1970 console log hashT retrieve  Alex Hawkins        510-599-1930 console log hashT retrieve  Lebron James        null

User · Answer

You can create one using like the following   x000D   x000D  var dictionary     Name  Some Programmer   Age 24  Job  Writing Programs          Iterate over using keys for  var key in dictionary      console log  Key      key            Value     dictionary key          Access a key using object notation  console log  Her name is      dictionary Name  x000D   x000D   x000D

[javascript] How to do associative array/hashing in JavaScript

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