Convert Array to Object

Question

What is the best way to convert     a   b   c     to       0   a     1   b     2   c

User · Answer

I would do this simply with Array of    Array of has the ability to use it s context as a constructor      NOTE 2 The of function is an intentionally generic factory method  it   does not require that its this value be the Array constructor    Therefore it can be transferred to or inherited by other constructors   that may be called with a single numeric argument    So we may bind Array of   to a function and generate an array like object    x000D   x000D  function dummy      x000D  var thingy   Array of apply dummy  1 2 3 4    x000D  console log thingy   x000D   x000D   x000D    By utilizing Array of   one can even do array sub-classing

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For completeness  ECMAScript 2015 ES6  spreading  Will require either a transpiler Babel  or an environment running at least ES6    x000D   x000D  console log  x000D            a    b    c     x000D    x000D   x000D   x000D

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Five years later  there s a good way     Object assign was introduced in ECMAScript 2015   Object assign       a    b    c         0   a    1   b    2   c

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x000D   x000D  let i   0  x000D  let myArray     first    second    third    fourth    x000D   x000D  const arrayToObject    arr    gt  x000D      Object assign        arr map item   gt     i     item      x000D   x000D  console log arrayToObject myArray    x000D   x000D   x000D    Or use   x000D   x000D  myArray     first    second    third    fourth   x000D  console log     myArray   x000D   x000D   x000D

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you can use spread operator  x    1 2 3 10      x      0 1  1 2  2 3  3 10

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x000D   x000D  var finalResult     a   b   c   map  item   index    gt     index    item     x000D  console log finalResult  x000D   x000D   x000D

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Below method would convert array to object with particular given key                  Converts array to object         param   Array  array         param   string  key  optional              Array prototype ArrayToObject   function key           const array   this         const obj               array forEach  element  index    gt               if  key                  obj index    element               else if   element  amp  amp  typeof element     object   amp  amp  element key                    obj element key     element                              return obj          For Ex -    name   test     name   test1    ArrayToObject  name     would give    test   name   test    test1   name   test1      and incase key is not provided as param to the method  i e    name   test     name   test1    ArrayToObject      would give    0   name   test    1   name   test1

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we can use Object assign and array reduce function to convert an Array to Object   x000D   x000D  var arr     a  b 1    c  d 2     x000D  var newObj   arr reduce  a  b    gt  Object assign a  b       x000D   x000D  console log newObj  x000D   x000D   x000D

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Quick and dirty  2  var i   0     s          a     A    B    C     while  i  lt  a length     s i    a i

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A more OO approach     Array prototype toObject   function      var Obj       for var i in this      if typeof this i      function          Logic here    Obj i  this i            return Obj

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You could use an accumulator aka reduce     a   b   c   reduce function result  item  index  array      result index    item    a  b  c   return result           watch out the empty     which is passed as  result    Pass an empty object    as a starting point  then  augment  that object incrementally  At the end of the iterations  result will be   0    a    1    b    2    c    If your array is a set of key-value pair objects      a  1    b  2    c  3   reduce function result  item      var key   Object keys item  0     first property  a  b  c   result key    item key     return result            will produce   a  1  b  2  c  3   For the sake of completeness  reduceRight allows you to iterate over your array in reverse order      a  1    b  2    c  3   reduceRight    same implementation as above       will produce   c 3  b 2  a 1   Your accumulator can be of any type for you specific purpose  For example in order to swap the key and value of your object in an array  pass         a  1    b  2    c  3   reduce function result  item  index      var key   Object keys item  0     first property  a  b  c   var value   item key     var obj         obj value    key    result push obj     return result            an empty array   will produce    1   a     2   b     3   c     Unlike map  reduce may not be used as a 1-1 mapping  You have full control over the items you want to include or exclude  Therefore reduce allows you to achieve what filter does  which makes reduce very versatile      a  1    b  2    c  3   reduce function result  item  index      if index     0      skip the first item     result push item         return result            an empty array   will produce    2   b     3   c     Caution  reduce and Object key are part of ECMA 5th edition  you should provide a polyfill for browsers that don t support them  notably IE8    See a default implementation by Mozilla

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For ES2016  spread operator for objects  Note  This is after ES6 and so transpiler will need to be adjusted     x000D   x000D  const arr     a    b    c    x000D  const obj       arr      - gt   0   a   1   b   2   c    x000D   x000D   x000D

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reduce  o v i   gt  o i  v o          docs   or more verbose  var trAr2Obj   function  arr   return arr reduce  o v i   gt  o i  v o           or  var transposeAr2Obj   arr  gt arr reduce  o v i   gt  o i  v o         shortest one with vanilla JS  JSON stringify    a    X      b    Y    reduce  o v i   gt  return o i  v o          gt     0    a   X    1    b   Y       some more complex example     a    X      b    Y    reduce  o v i   gt  return o v 0   v slice 1  0  o         gt  Object  a   X   b   Y     even shorter  by using function e   console log e   return e        e   gt  console log e  e      nodejs  gt    1  2  3    3 4 5   reduce  o v i   gt  o v 0   v slice 1  o          1     2  3     3     4  5         docs

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I ended up using object spread operator  since it is part of the ECMAScript 2015  ES6  standard   const array     a    b    c    console log     array       it outputs  0  a   1  b   2  c     Made the following fiddle as an example

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If you can use Map or Object assign  it s very easy   Create an array   const languages     css    javascript    php    html      The below creates an object with index as keys   Object assign     languages    Replicate the same as above with Maps  Converts to an index based object  0    css   etc     const indexMap   new Map languages map  name  i    gt   i  name      indexMap get 1     javascript   Convert to an value based object  css    css is great   etc     const valueMap   new Map languages map name   gt   name     name  is great        valueMap get  css      css is great

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If you like oneliners  and IE8 is not a problem anymore  as it should be     a   b   c   reduce  m e i    gt  Object assign m    i   e           Go ahead and try it on the browser console  It coult be more verbose like this     a   b   c   reduce function memo elm idx        return Object assign memo    idx   elm              But still rules out IE8  If IE8 is a must  then you can use lodash underscore like that     reduce   a   b   c    function memo elm idx        return Object assign memo    idx   elm

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maybe if you want array value to be your object key too  function toObject arr      var rv         for  var i   0  i  lt  arr length    i      rv arr i     arr i     return rv

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Here s a solution in coffeescript  arrayToObj    arr  - gt    obj        for v i in arr     obj i    v if v    obj

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My version array to json in JS  Jusy copy paste and use it  Isn t this awesome  I love this type of functions I found on StackOverflow    function array2json arr        var parts           var is list    Object prototype toString apply arr        object Array          for var key in arr            var value   arr key           if typeof value     object       Custom handling for arrays             if is list  parts push array2json value        RECURSION                 else parts key    array2json value       RECURSION               else               var str                   if  is list  str         key                        Custom handling for multiple data types             if typeof value     number   str    value    Numbers             else if value     false  str     false     The booleans             else if value     true  str     true               else str          value          All other things                 TODO  Is there any more datatype we should be in the lookout for   Functions                parts push str                       var json   parts join            if is list  return       json         Return numerical JSON     return       json         Return associative JSON

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FWIW  one another recent approach is to use the new Object fromEntries along with Object entries as follows  const arr     a   b   c    arr -2     d   arr hello    e   arr length   17  const obj   Object fromEntries Object entries arr        which allows for avoiding storing sparse array items as undefined or null and preserves non-index  e g   non-positive-integer non-numeric  keys     0   quot a quot   1   quot b quot   2   quot c quot    quot -2 quot    quot d quot   hello   quot e quot      Same result here as with  Paul Draper s Object assign answer   One may wish to add arr length  however  as that is not included  obj length   arr length

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ECMAScript 6 introduces the easily polyfillable Object assign   The Object assign   method is used to copy the values of all enumerable own properties from one or more source objects to a target object  It will return the target object   Object assign       a   b   c         0  quot a quot   1  quot b quot   2  quot c quot    The own length property of the array is not copied because it isn t enumerable  Also  you can use ES8 spread syntax on objects to achieve the same result         a    b    c

User · Answer

I would use underscore for this  but if that isn t available then I would drop down to using reduce with an initial value of empty object      gt  gt  gt    a    b    c   reduce function p  c  i   p i    c  return p       Object   0  a   1  b   2  c     reduce should be widely available in most browsers today  see MDN

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If you re using ES6  you can use Object assign and the spread operator         a    b    c       If you have nested array like  var arr   1 2 3 4   Object assign    arr map d   gt     d 0    d 1

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If you are using angularjs you can use angular extend  the same effect with   extend of jquery   var newObj       angular extend newObj    a   b   c

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Here s a recursive function I just wrote  It s simple and works well      Convert array to object var convArrToObj   function array       var thisEleObj   new Object        if typeof array     object            for var i in array               var thisEle   convArrToObj array i                thisEleObj i    thisEle                 else           thisEleObj   array            return thisEleObj      Here s an example  jsFiddle    var array   new Array    array a   123  array b   234  array c   345  var array2   new Array    array2 a   321  array2 b   432  array2 c   543  var array3   new Array    array3 a   132  array3 b   243  array3 c   354  var array4   new Array    array4 a   312  array4 b   423  array4 c   534  var array5   new Array    array5 a   112  array5 b   223  array5 c   334   array d   array2  array4 d   array5  array3 d   array4  array e   array3    console log array       Convert array to object var convArrToObj   function array       var thisEleObj   new Object        if typeof array     object            for var i in array               var thisEle   convArrToObj array i                thisEleObj i    thisEle                 else           thisEleObj   array            return thisEleObj    console log convArrToObj array      Results

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A quick and dirty one   var obj         arr     a   b   c      l   arr length    while  l  amp  amp   obj --l    arr pop

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Simplest way to do this is the following    const arr     a   b   c    let obj       function ConvertArr arr      if  typeof arr       array      Object assign obj  arr       This way it only runs if it is an array  however  you can run this with let global object variable or without  that s up to you  if you run without let  just do Object assign     arr

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You could use a function like this   var toObject   function array        var o           for  var property in array            if  String property  gt  gt  gt  0     property  amp  amp  property  gt  gt  gt  0    0xffffffff                o i    array i                       return o       This one should handle sparse arrays more efficiently

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A simple and cheeky method of quickly converting an Array of items in to an Object  function arrayToObject  srcArray        return  JSON parse  JSON stringify  srcArray          Then using it like so     var p    0 2 3  pork   pie  6   obj   new arrayToObject  p    console log  obj 3   obj 4       expecting  pork pie    Output    pork pie   Checking the type   typeof obj  object    AND things wouldn t be complete if there wasn t a prototype method   Array prototype toObject  function        return  JSON parse  JSON stringify  this          Using like   var q    0 2 3  cheese   whizz  6   obj   q toObject    console log  obj 3   obj 4       expecting  cheese whizz    Output   cheese whizz    NOTE that there is no naming routine  so if you want to have specific names  then you will need to continue using the existing methods below     Older method  This allows you to generate from an array an object with keys you define in the order you want them    Array prototype toObject   function keys       var obj           var tmp   this     we want the original array intact      if keys length    this length           var c   this length-1          while  c gt  0                obj  keys  c       tmp c               c--                      return obj      result     cheese   paint  14 8  toObject  0  onion  4 99      console log   gt  gt  gt       result onion   will output  paint   the function has to have arrays of equal length or you get an empty object   Here is an updated method  Array prototype toObject   function keys       var obj           if  keys length    this length          while  keys length               obj  keys pop       this  keys length        return obj

User · Answer

With a function like this   function toObject arr      var rv         for  var i   0  i  lt  arr length    i      rv i    arr i     return rv      Your array already is more-or-less just an object  but arrays do have some  interesting  and special behavior with respect to integer-named properties  The above will give you a plain object   edit oh also you might want to account for  holes  in the array   function toObject arr      var rv         for  var i   0  i  lt  arr length    i      if  arr i      undefined  rv i    arr i     return rv      In modern JavaScript runtimes  you can use the  reduce   method   var obj   arr reduce function acc  cur  i      acc i    cur    return acc            That one also avoids  holes  in the array  because that s how  reduce   works

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It is easy to use javascript reduce     a    b    c    d   reduce function previousValue  currentValue  index        previousValue index    currentValue      return previousValue              You can take a look at Array prototype reduce    https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Array Reduce

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It s not directly relevant but I came here searching for a one liner for merging nested objects such as   const nodes         node1            interfaces   if1      if2                 node2            interfaces   if3      if4                 node3            interfaces   if5      if6                 The solution is to use a combination of reduce and object spread   const allInterfaces   nodes   gt  Object keys nodes  reduce  res  key    gt       res     nodes key  interfaces

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Using  javascript forEach one can do this  var result           attributes     a    b   c     attributes forEach function prop index      result index    prop        With ECMA6   attributes forEach  prop index   gt result index    prop

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If you re using jquery     extend       a    b    c

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I have faced this issue multiple times and decided to write a function that is as generic as possible  Have a look and feel free to modify anything  function typeOf obj        if   typeof obj      object              if  obj length              return  array           else             return  object         else     return typeof obj      function objToArray obj  ignoreKeys        var arr           if  typeOf obj      object             for  var key in obj                if  typeOf obj key       object                     if  ignoreKeys                      arr push objToArray obj key  ignoreKeys                    else                     arr push  key objToArray obj key                                else                 arr push obj key                   else if  typeOf obj      array             for  var key 0 key lt obj length key                  if  typeOf obj key       object                   arr push objToArray obj key                 else                 arr push obj key                        return arr

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Try using reflect to copy from array item to object   var arr    aa 23   bb 44   cc 55       var obj         arr forEach e   gt            var ee   e split              Reflect set obj ee 0  ee 1               console log obj       aa   23   bb   44   cc   55

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Surprised not to see -   x000D   x000D  console log  x000D    Object assign       a    b    c    x000D    x000D   x000D   x000D

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As of Lodash 3 0 0 you can use   toPlainObject   x000D   x000D  var obj     toPlainObject   a    b    c     x000D  console log obj   x000D   lt script src  https   cdn jsdelivr net lodash 4 16 4 lodash min js  gt  lt  script gt  x000D   x000D   x000D

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More browser supported and more flexible way of doing that is using a normal loop  something like   const arr     a    b    c    obj        for  let i 0  i lt arr length  i         obj i    arr i       But also the modern way could be using the spread operator  like        arr    Or Object assign   Object assign       a    b    c       Both will return    0   a   1   b   2   c

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ES5 - Solution   Using Array prototype function  push  and  apply  you can populate the object with the array elements    x000D   x000D  var arr     a   b   c    x000D  var obj   new Object    x000D  Array prototype push apply obj  arr   x000D  console log obj            0    a    1    b    2    c   length  3   x000D  console log obj 2       c x000D   x000D   x000D

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Object assign       one    two         0   one   1   two     Easy way in modern JavaScript is to use Object assign   that does nothing but copying key value from one object to another  In our case  Array donates properties to new

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initial array and will convert into an Object with keys which will be the unique element of an array and the keys value will be how many times the perticular keys will be repeating   x000D   x000D  var jsTechs     angular    react    ember    vanilaJS    ember    angular    react    ember    vanilaJS    angular    react    ember    vanilaJS    ember    angular    react    ember    vanilaJS    ember    angular    react    ember    vanilaJS    ember    react    react    vanilaJS    react    vanilaJS    vanilaJS   x000D   x000D  var initialValue     x000D    java   4 x000D    x000D   x000D  var reducerFunc   function reducerFunc  initObj  jsLib    x000D    if   initObj jsLib     x000D      initObj jsLib    1 x000D      else   x000D      initObj jsLib     1 x000D      x000D    return initObj x000D    x000D  var finalResult   jsTechs reduce reducerFunc  initialValue  x000D  console log finalResult  x000D   x000D   x000D

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Here is an O 1  ES2015 method just for completeness   var arr    1  2  3  4  5      array  already an object Object setPrototypeOf arr  Object prototype      now no longer an array  still an object

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Use the javascript lodash library  There is a simple method    mapKeys object   iteratee   identity    that can do the conversion

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I d probably write it this way  since very rarely I ll not be having the underscorejs library at hand    var     require  underscore     var a      a    b    c     var obj     extend     a   console log obj      prints    0    a    1    b    2    c

[javascript] Convert Array to Object

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