Javascript swap array elements

Question

Is there any simpler way to swap two elements in an array   var a   list x   b   list y   list y    a  list x    b

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Swap the first and last element in an array without temporary variable or ES6 swap method  a  b     b  a    a pop       a slice 1   a shift

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You can swap elements in an array the following way   list x     list y  list y  list x   0    See the following example   list    1 2 3 4 5  list 1     list 3  list 3  list 1   0    list is now  1 4 3 2 5    Note  it works the same way for regular variables  var a 1 b 5  a    b b a  0

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For the sake of brevity  here s the ugly one-liner version that s only slightly less ugly than all that concat and slicing above  The accepted answer is truly the way to go and way more readable    Given   var foo     0  1  2  3  4  5  6      if you want to swap the values of two indices  a and b   then this would do it   foo splice  a  1  foo splice b 1 foo a   0       For example  if you want to swap the 3 and 5  you could do it this way   foo splice  3  1  foo splice 5 1 foo 3   0       or   foo splice  5  1  foo splice 3 1 foo 5   0       Both yield the same result   console log  foo         gt    0  1  2  5  4  3  6      splicehatersarepunks

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Here is a variation that first checks if the index exists in the array   Array prototype swapItems   function a  b       if     a in this       b in this            return this      this a    this splice b  1  this a   0       return this      It currently will just return this if the index does not exist  but you could easily modify behavior on fail

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Consider such a solution without a need to define the third variable    x000D   x000D  function swap arr  from  to    x000D    arr splice from  1  arr splice to  1  arr from   0    x000D    x000D   x000D  var letters     a    b    c    d    e    f    x000D   x000D  swap letters  1  4   x000D   x000D  console log letters        a    e    c    d    b    f   x000D   x000D   x000D    Note  You may want to add additional checks for example for array length  This solution is mutable so swap function does not need to return a new array  it just does mutation over array passed into

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Here s a one-liner that doesn t mutate list   let newList   Object assign     list    x   list y    y   list x      Uses language features not available in 2009 when the question was posted

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Flow not inplace solution let swap   arr i j   gt  arr map  e k   gt  k-i    k-j   e   arr i     arr j      x000D   x000D  let swap   arr i j   gt  arr map  e k   gt  k-i    k-j   e   arr i     arr j         test index  3 lt - gt 5     f  lt - gt  d   let a    a   b   c   d   e   f   g    let b  swap a 3 5    console log a   n   b   console log  Example Flow    swap a 3 5  reverse   join  -      x000D   x000D   x000D   and inplace solution  x000D   x000D  let swap   arr i j   gt   let t arr i   arr i  arr j   arr j  t  return arr       test index  3 lt - gt 5     f  lt - gt  d   let a    a   b   c   d   e   f   g     console log  swap a 3 5    console log  Example Flow    swap a 3 5  reverse   join  -      x000D   x000D   x000D   In this solutions we use  quot flow pattern quot  which means that swap function returns array as result - this allow to easily continue processing using dot    like reverse and join in snippets

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According to some random person on Metafilter   Recent versions of Javascript allow you to do swaps  among other things  much more neatly      list x   list y        list y   list x       My quick tests showed that this Pythonic code works great in the version of JavaScript currently used in  Google Apps Script     gs    Alas  further tests show this code gives a  Uncaught ReferenceError  Invalid left-hand side in assignment   in whatever version of JavaScript    js   is used by Google Chrome Version 24 0 1312 57 m

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You only need one temporary variable   var b   list y   list y    list x   list x    b      Edit hijacking top answer 10 years later with a lot of ES6 adoption under our belts   Given the array arr    1 2 3 4   you can swap values in one line now like so    arr 0   arr 1      arr 1   arr 0      This would produce the array  2 1 3 4   This is destructuring assignment

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what about Destructuring assignment  var arr    1  2  3  4   arr index1   arr index2      arr index2   arr index1     which can also be extended to   src order elements    gt   dest order elements

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Well  you don t need to buffer both values - only one   var tmp   list x   list x    list y   list y    tmp

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If you don t want to use temp variable in ES5  this is one way to swap array elements   var swapArrayElements   function  a  x  y      if  a length     1  return a    a splice y  1  a splice x  1  a y   0      return a      swapArrayElements  1  2  3  4  5   1  3       gt    1  4  3  2  5

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try this function      x000D   x000D    document  ready function      x000D          var pair       x000D          var destinationarray     AAA   BBB   CCC    x000D   x000D          var cityItems   getCityList destinationarray   x000D          for  var i   0  i  lt  cityItems length  i      x000D              pair       x000D              var ending point       x000D              for  var j   0  j  lt  cityItems i  length  j      x000D                  pair push cityItems i  j    x000D                x000D              alert pair   x000D              console log pair  x000D            x000D   x000D          x000D      function getCityList inputArray    x000D          var Util   function      x000D             x000D   x000D          Util getPermuts   function  array  start  output    x000D              if  start  gt   array length    x000D                  var arr   array slice 0   x000D                  output push arr   x000D                else   x000D                  var i  x000D   x000D                  for  i   start  i  lt  array length    i    x000D                      Util swap array  start  i   x000D                      Util getPermuts array  start   1  output   x000D                      Util swap array  start  i   x000D                    x000D                x000D            x000D   x000D          Util getAllPossiblePermuts   function  array  output    x000D              Util getPermuts array  0  output   x000D            x000D   x000D          Util swap   function  array  from  to    x000D              var tmp   array from   x000D              array from    array to   x000D              array to    tmp  x000D            x000D          var output       x000D          Util getAllPossiblePermuts inputArray  output   x000D          return output  x000D        x000D   lt script src  https   ajax googleapis com ajax libs jquery 2 1 1 jquery min js  gt  lt  script gt  x000D   x000D   x000D

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There is one interesting way of swapping   var a   1  var b   2   a b     b a      ES6 way

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function moveElement array  sourceIndex  destinationIndex        return array map a   gt  a id     sourceIndex   array find a   gt  a id     destinationIndex   a id     destinationIndex   array find a   gt  a id     sourceIndex    a     let arr      id   quot 1 quot  title   quot abc1 quot     id   quot 2 quot  title   quot abc2 quot     id   quot 3 quot  title   quot abc3 quot     id   quot 4 quot  title   quot abc4 quot      moveElement arr   quot 2 quot   quot 4 quot

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x000D   x000D  var arr    1  2   x000D  arr splice 0  2  arr 1   arr 0    x000D  console log arr      2  1  x000D   x000D   x000D

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For two or more elements  fixed number   list y   list x      list x   list y     No temporary variable required  I was thinking about simply calling list reverse    But then I realised it would work as swap only when list length   x   y   1  For variable number of elements I have looked into various modern Javascript constructions to this effect  including Map and map  but sadly none has resulted in a code that was more compact or faster than this old-fashioned  loop-based construction   x000D   x000D  function multiswap arr i0 i1      argument immutable if string        if  arr split  return multiswap arr split      i0  i1  join          var diff           for  let i in i0  diff i0 i     arr i1 i        return Object assign arr diff      Example      var alphabet    abcdefghijklmnopqrstuvwxyz       var  x y z     14 6 15       var output   document getElementsByTagName  code        output 0  innerHTML   alphabet      output 1  innerHTML   multiswap alphabet   0 25    25 0        output 2  innerHTML   multiswap alphabet   0 25 z 1 y x    25 0 x y z 3    x000D   lt table gt       lt tr gt  lt td gt Input  lt  td gt                          lt td gt  lt code gt  lt  code gt  lt  td gt  lt  tr gt       lt tr gt  lt td gt Swap two elements  lt  td gt              lt td gt  lt code gt  lt  code gt  lt  td gt  lt  tr gt       lt tr gt  lt td gt Swap multiple elements  amp nbsp  lt  td gt   lt td gt  lt code gt  lt  code gt  lt  td gt  lt  tr gt   lt  table gt  x000D   x000D   x000D

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Using ES6 it s possible to do it like this     Imagine you have these 2 arrays     const a     a    b    c    d    e    const b    5  4  3  2  1     and you want to swap the first values   const  a0    a  a 0    b 0   b 0    a0    and value   a     5   b    c    d    e   b      a   4  3  2  1

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Here s a compact version  swaps value at i1 with i2 in arr  arr slice 0 i1  concat arr i2  arr slice i1 1 i2  arr i1  arr slice i2 1

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This didn t exist when the question was asked  but ES2015 introduced array destructuring  allowing you to write it as follows   let a   1  b   2     a  1  b  2  a  b     b  a      a  2  b  1

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Array prototype swap   function a  b      var temp   this a     this a    this b     this b    temp       Usage    var myArray    0 1 2 3 4      myArray swap 4 1

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If need swap first and last elements only   array unshift  array pop

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To swap two consecutive elements of array  array splice IndexToSwap 2 array IndexToSwap 1  array IndexToSwap

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You can swap any number of objects or literals  even of different types  using a simple identity function like this   var swap   function  x  return x   b   swap a  a b   c   swap a  a b  b c     For your problem   var swap   function  x  return x   list y     swap list x   list x  list y      This works in JavaScript because it accepts additional arguments even if they are not declared or used   The assignments a b etc  happen after a is passed into the function

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Typescript solution that clones the array instead of mutating existing one  export function swapItemsInArray lt T gt  items  T    indexA  number  indexB  number   T       const itemA   items indexA      const clone       items      clone indexA    clone indexB     clone indexB    itemA     return clone

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With numeric values you can avoid a temporary variable by using bitwise xor  list x    list x    list y   list y    list y    list x   list x    list x    list y     or an arithmetic sum  noting that this only works if x   y is less than the maximum value for the data type   list x    list x    list y   list y    list x  - list y   list x    list x  - list y

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Digest from http   www greywyvern com  post 265  var a   5  b   9      b    a    b -  a  - b      alert  a  b       alerts  9  5

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This seems ok      var b   list y   list y    list x   list x    b    Howerver using   var b   list y     means a b variable is going to be to be present for the rest of the scope  This can potentially lead to a memory leak  Unlikely  but still better to avoid   Maybe a good idea to put this into Array prototype swap  Array prototype swap   function  x y      var b   this x     this x    this y     this y    b    return this      which can be called like   list swap  x  y     This is a clean approach to both avoiding memory leaks and DRY

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Just for the fun of it  another way without using any extra variable would be    x000D   x000D  var arr    1  2  3  4  5  6  7  8  9   x000D   x000D     swap index 0 and 2 x000D  arr arr length    arr 0        copy idx1 to the end of the array x000D  arr 0    arr 2                 copy idx2 to idx1 x000D  arr 2    arr arr length-1      copy idx1 to idx2 x000D  arr length--                   remove idx1  was added to the end of the array  x000D   x000D   x000D  console log  arr       - gt   3  2  1  4  5  6  7  8  9  x000D   x000D   x000D

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If you want a single expression  using native javascript   remember that the return value from a splice operation  contains the element s  that was removed   var A    1  2  3  4  5  6  7  8  9   x  0  y  1  A x    A splice y  1  A x   0   alert A      alerts  2 1 3 4 5 6 7 8 9    Edit   The  0  is necessary at the end of the expression as Array splice   returns an array  and in this situation we require the single element in the returned array

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var a    1 2 3 4 5   b a length   for  var i 0  i lt b  i          a unshift a splice 1 i 1  shift       a shift      a    5 4 3 2 1

[javascript] Javascript swap array elements

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