Iterate over a Javascript associative array in sorted order

Question

Let s say I have a Javascript associative array  a k a  hash  a k a  dictionary    var a   new Array    a  b     1  a  z     1  a  a     1    How can I iterate over the keys in sorted order  If it helps simplify things  I don t even need the values  they re all just the number 1

User · Answer

Get the keys in the first for loop  sort it  use the sorted result in the 2nd for loop   var a   new Array    a  b     1  a  z     1  a  a     1   var b       for  k in a  b push k   b sort    for  var i   0  i  lt  b length    i  alert b i

User · Answer

x000D   x000D  var a   new Array    x000D  a  b     1  x000D  a  z     1  x000D  a  a     1  x000D   x000D   x000D  var keys Object keys a  sort    x000D  for var i 0 key keys 0  i lt keys length key keys   i    x000D    document write key       a key    lt br gt     x000D    x000D   x000D   x000D

User · Answer

You can use the keys function from the underscore js library to get the keys  then the sort   array method to sort them   var sortedKeys     keys dict  sort      The keys function in the underscore s source code      Retrieve the names of an object s properties     Delegates to   ECMAScript 5   s native  Object keys    keys   nativeKeys    function obj        if  obj     Object obj   throw new TypeError  Invalid object        var keys           for  var key in obj  if    has obj  key   keys push key       return keys             Shortcut function for checking if an object has a given property directly    on itself  in other words  not on a prototype     has   function obj  key        return hasOwnProperty call obj  key

User · Answer

You can use the Object keys built-in method   var sorted keys   Object keys a  sort      Note  this does not work in very old browsers not supporting EcmaScript5  notably IE6  7 and 8  For detailed up-to-date statistics  see this table

User · Answer

You cannot iterate over them directly  but you can find all the keys and then just sort them   var a   new Array    a  b     1  a  z     1  a  a     1       function keys obj        var keys            for var key in obj                if obj hasOwnProperty key                         keys push key                        return keys     keys a  sort         a    b    z     However there is no need to make the variable  a  an array   You are really just using it as an object and should create it like this   var a       a  key      value

User · Answer

There s no concise way to directly manipulate the  keys  of a Javascript object  It s not really designed for that  Do you have the freedom to put your data in something better than a regular object  or an Array  as your sample code suggests    If so  and if your question could be rephrased as  What dictionary-like object should I use if I want to iterate over the keys in sorted order   then you might develop an object like this   var a       keys   new Array      hash   new Object      set   function key  value        if  typeof this hash key       undefined     this keys push key         this hash key    value         get   function key        return this hash key          getSortedKeys   function         this keys sort        return this keys             sample use a set  b  1   a set  z  1   a set  a  1   var sortedKeys   a getSortedKeys    for  var i in sortedKeys    print sortedKeys i        If you have no control over the fact that the data is in a regular object  this utility would convert the regular object to your fully-functional dictionary   a importObject   function object      for  var i in object    this set i  object          This was a object definition  instead of a reusable constructor function  for simplicity  edit at will

User · Answer

lt script type  text javascript  gt      var a             b 1          z 1          a 1           your JS Object     var keys           for  key in a            keys push key             keys sort        var i   0      var keyslen   keys length      var str             SORTED KEY ITERATION     while  i  lt  keyslen            str    keys i       gt     a keys i       n             i            alert str         RESULT      a  gt 1     b  gt 1     z  gt 1         lt  script gt

User · Answer

I really like  luke-schafer s prototype idea  but also hear what he is saying about the issues with prototypes  What about using a simple function     x000D   x000D  function sortKeysAndDo  obj  worker     x000D    var keys   Object keys obj   x000D    keys sort    x000D    for  var i   0  i  lt  keys length  i      x000D       worker keys i   obj keys i     x000D      x000D    x000D   x000D  function show  key  value     x000D    document write  key           value    lt br gt      x000D    x000D   x000D  var a   new Array    x000D  a  b     1  x000D  a  z     1  x000D  a  a     1  x000D   x000D  sortKeysAndDo  a  show   x000D   x000D  var my object      c   3   a   1   b   2    x000D   x000D  sortKeysAndDo  my object  show   x000D   x000D   x000D    This seems to eliminate the issues with prototypes and still provide a sorted iterator for objects  I am not really a JavaScript guru  though  so I d love to know if this solution has hidden flaws I missed

User · Answer

I agree with Swingley s answer  and I think it is an important point a lot of these more elaborate solutions are missing  If you are only concerned with the keys in the associative array and all the values are  1   then simply store the  keys  as values in an array   Instead of   var a     b 1  z 1  a 1       relatively elaborate code to retrieve the keys and sort them   Use   var a      b    z    a     alert a sort       The one drawback to this is that you can not determine whether a specific key is set as easily  See this answer to javascript function inArray for an answer to that problem  One issue with the solution presented is that a hasValue  key   is going to be slightly slower than a  key    That may or may not matter in your code

User · Answer

you could even prototype it onto object   Object prototype iterateSorted   function worker        var keys           for  var key in this                if  this hasOwnProperty key               keys push key             keys sort         for  var i   0  i  lt  keys length  i                  worker this  keys i                and the usage   var myObj     a 1  b 2    myObj iterateSorted function value        alert value

[javascript] Iterate over a Javascript associative array in sorted order

Examples related to javascript