Simplest code for array intersection in javascript

Question

What s the simplest  library-free code for implementing array intersections in javascript  I want to write  intersection  1 2 3    2 3 4 5     and get   2  3

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x000D   x000D     Return elements of array a that are also in b in linear time  x000D  function intersect a  b    x000D    return a filter Set prototype has  new Set b    x000D    x000D   x000D     Example  x000D  console log intersect  1 2 3    2 3 4 5     x000D   x000D   x000D    I recommend above succinct solution which outperforms other implementations on large inputs  If performance on small inputs matters  check the alternatives below   Alternatives and performance comparison   See the following snippet for alternative implementations and check https   jsperf com array-intersection-comparison for performance comparisons    x000D   x000D  function intersect for a  b    x000D    const result       x000D    const alen   a length  x000D    const blen   b length  x000D    for  let i   0  i  lt  alen    i    x000D      const ai   a i   x000D      for  let j   0  j  lt  blen    j    x000D        if  ai     b j     x000D          result push ai   x000D          break  x000D          x000D        x000D       x000D    return result  x000D    x000D   x000D  function intersect filter indexOf a  b    x000D    return a filter el   gt  b indexOf el      -1   x000D    x000D   x000D  function intersect filter in a  b    x000D    const map   b reduce  map  el    gt   map el    true  return map        x000D    return a filter el   gt  el in map   x000D    x000D   x000D  function intersect for in a  b    x000D    const result       x000D    const map       x000D    for  let i   0  length   b length  i  lt  length    i    x000D      map b i     true  x000D      x000D    for  let i   0  length   a length  i  lt  length    i    x000D      if  a i  in map  result push a i    x000D      x000D    return result  x000D    x000D   x000D  function intersect filter includes a  b    x000D    return a filter el   gt  b includes el    x000D    x000D   x000D  function intersect filter has this a  b    x000D    return a filter Set prototype has  new Set b    x000D    x000D   x000D  function intersect filter has arrow a  b    x000D    const set   new Set b   x000D    return a filter el   gt  set has el    x000D    x000D   x000D  function intersect for has a  b    x000D    const result       x000D    const set   new Set b   x000D    for  let i   0  length   a length  i  lt  length    i    x000D      if  set has a i    result push a i    x000D      x000D    return result  x000D    x000D   x000D   x000D    Results in Firefox 53    Ops sec on large arrays  10 000 elements    filter   has  this                523  this answer  for   has                         482 for-loop   in                     279 filter   in                       242 for-loops                          24 filter   includes                  14 filter   indexOf                   10  Ops sec on small arrays  100 elements    for-loop   in                 384 426 filter   in                   192 066 for-loops                     159 137 filter   includes             104 068 filter   indexOf               71 598 filter   has  this             43 531  this answer  filter   has  arrow function   35 588

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Use a combination of Array prototype filter and Array prototype includes  const filteredArray   array1 filter value   gt  array2 includes value     For older browsers  with Array prototype indexOf and without an arrow function  var filteredArray   array1 filter function n        return array2 indexOf n      -1       NB  Both  includes and  indexOf internally compares elements in the array by using      so if the array contains objects it will only compare object references  not their content   If you want to specify your own comparison logic  use  some instead

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If you need to have it handle intersecting multiple arrays   x000D   x000D  const intersect    a1  a2     rest    gt      const a12   a1 filter value   gt  a2 includes value     if  rest length     0    return a12      return intersect a12     rest       console log intersect  1 2 3 4 5    1 2    1  2  3 4 5    2  10  1     x000D   x000D   x000D

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function intersection A B   var result   new Array    for  i 0  i lt A length  i          for  j 0  j lt B length  j              if  A i     B j   amp  amp    inArray A i  result     -1                result push A i                      return result

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If your arrays are sorted  this should run in O n   where n is min  a length  b length    function intersect 1d  a  b        var out     ai 0  bi 0  acurr  bcurr  last Number MIN SAFE INTEGER      while    acurr a ai      undefined  amp  amp    bcurr b bi      undefined            if  acurr  lt  bcurr               if  last   acurr                    out push  acurr                              last acurr              ai                      else if  acurr  gt  bcurr               if  last   bcurr                    out push  bcurr                              last bcurr              bi                      else               out push  acurr                last acurr              ai                bi                        return out

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Sort it check one by one from the index 0  create new array from that    Something like this  Not tested well though   function intersection x y    x sort   y sort     var i j 0 ret      while i lt x length  amp  amp  j lt y length     if x i  lt y j  i      else if y j  lt x i  j      else      ret push x i       i   j            return ret     alert intersection  1 2 3    2 3 4 5       PS The algorithm only intended for Numbers and Normal Strings  intersection of arbitary object arrays may not work

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filter  and  indexOf  aren t supported on Array in IE  How about this   var array1    1  2  3   var array2    2  3  4  5    var intersection       for  i in array1        for  j in array2            if  array1 i     array2 j   intersection push array1 i

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Using jQuery   var a    1 2 3   var b    2 3 4 5   var c     b  not   b  not a    alert c

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If your environment supports ECMAScript 6 Set  one simple and supposedly efficient  see specification link  way   function intersect a  b      var setA   new Set a     var setB   new Set b     var intersection   new Set     setA  filter x   gt  setB has x       return Array from intersection       Shorter  but less readable  also without creating the additional intersection Set    function intersect a  b      var setB   new Set b     return     new Set a   filter x   gt  setB has x        Note that when using sets you will only get distinct values  thus new Set  1  2  3  3   size evaluates to 3

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function getIntersection arr1  arr2       var result           arr1 forEach function elem           arr2 forEach function elem2               if elem     elem2                   result push elem                                         return result     getIntersection  1 2 3    2 3 4 5         2  3

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Here s a very naive implementation I m using  It s non-destructive and also makes sure not to duplicate entires   Array prototype contains   function elem        return this indexOf elem   gt  -1       Array prototype intersect   function  array            this is naive--could use some optimization     var result           for   var i   0  i  lt  this length  i               if   array contains this i    amp  amp   result contains this i                 result push  this i               return result

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reduce to build a map  and  filter to find the intersection  delete within the  filter allows us to treat the second array as though it s a unique set   function intersection  a  b      var seen   a reduce function  h  k        h k    true      return h               return b filter function  k        var exists   seen k       delete seen k       return exists            I find this approach pretty easy to reason about  It performs in constant time

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Here is underscore js implementation     intersection   function array      if  array    null  return       var result         var argsLength   arguments length    for  var i   0  length   array length  i  lt  length  i          var item   array i       if    contains result  item   continue      for  var j   1  j  lt  argsLength  j            if     contains arguments j   item   break            if  j     argsLength  result push item         return result       Source  http   underscorejs org docs underscore html section-62

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For arrays containing only strings or numbers you can do something with sorting  as per some of the other answers  For the general case of arrays of arbitrary objects I don t think you can avoid doing it the long way  The following will give you the intersection of any number of arrays provided as parameters to arrayIntersection   var arrayContains   Array prototype indexOf       function arr  val            return arr indexOf val   gt  -1              function arr  val            var i   arr length          while  i--                if  arr i      val                    return true                                  return false          function arrayIntersection         var val  arrayCount  firstArray  i  j  intersection       missing      var arrays   Array prototype slice call arguments      Convert arguments into a real array         Search for common values     firstArray   arrays pop        if  firstArray            j   firstArray length          arrayCount   arrays length          while  j--                val   firstArray j               missing   false                  Check val is present in each remaining array              i   arrayCount              while   missing  amp  amp  i--                    if    arrayContains arrays i   val                          missing   true                                              if   missing                    intersection push val                                     return intersection     arrayIntersection   1  2  3   a     1   a   2     a   1        Gives  1   a

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Hope this Helps for all versions   function diffArray arr1  arr2      var newArr          var large   arr1 length gt  arr2 length arr1 arr2    var small   JSON stringify large     JSON stringify arr1  arr2 arr1    for var i 0 i lt large length i         var copyExists   false       for var j  0 j lt small length j           if large i   small j            copyExists  true          break                    if  copyExists                  newArr push large i                   for var i 0 i lt small length i         var copyExists   false       for var j  0 j lt large length j           if large j   small i            copyExists  true          break                    if  copyExists                  newArr push small i                    return newArr

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My contribution in ES6 terms  In general it finds the intersection of an array with indefinite number of arrays provided as arguments    x000D   x000D  Array prototype intersect   function    a    x000D    return  this    a  reduce  p c    gt  p filter e   gt  c includes e     x000D    x000D  var arrs     0 2 4 6 8   4 5 6 7   4 6    x000D       arr    0 1 2 3 4 5 6 7 8 9   x000D   x000D  document write   lt pre gt     JSON stringify arr intersect    arrs       lt  pre gt     x000D   x000D   x000D

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For simplicity      Usage const intersection   allLists    reduce intersect  allValues     reduce removeDuplicates            Implementation const intersect    intersection  list    gt    intersection filter item   gt      list some x   gt  x     item     const removeDuplicates    uniques  item    gt    uniques includes item    uniques   uniques concat item        Example Data const somePeople    bob  doug  jill   const otherPeople    sarah  bob  jill   const morePeople    jack  jill    const allPeople       somePeople     otherPeople     morePeople   const allGroups    somePeople  otherPeople  morePeople       Example Usage const intersection   allGroups    reduce intersect  allPeople     reduce removeDuplicates        intersection      jill    Benefits    dirt simple data-centric works for arbitrary number of lists works for arbitrary lengths of lists works for arbitrary types of values works for arbitrary sort order retains shape  order of first appearance in any array  exits early where possible memory safe  short of tampering with Function   Array prototypes   Drawbacks    higher memory usage higher CPU usage requires an understanding of reduce requires understanding of data flow   You wouldn t want to use this for 3D engine or kernel work  but if you have problems getting this to run in an event-based app  your design has bigger problems

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This is a modern and simple ES6 way to do it that is also very flexible  It lets you specify multiple arrays as the arrays to compare the subject array to  and can work in both inclusive and exclusive mode                                                The function                                             function assoc subjectArray  otherArrays    mustBeInAll   true             return subjectArray filter  subjectItem    gt        if  mustBeInAll          return otherArrays every  otherArray    gt          otherArray includes subjectItem                 else         return otherArrays some  otherArray    gt  otherArray includes subjectItem                                                                 The usage                                             const cheeseList     quot stilton quot    quot edam quot    quot cheddar quot    quot brie quot    const foodListCollection         quot cakes quot    quot ham quot    quot stilton quot        quot juice quot    quot wine quot    quot brie quot    quot bread quot    quot stilton quot          Output will be    stilton    brie   const inclusive   assoc cheeseList  foodListCollection    mustBeInAll  false         Output will be    stilton   const exclusive   assoc cheeseList  foodListCollection    mustBeInAll  true     Live example  https   codesandbox io s zealous-butterfly-h7dgf fontsize 14 amp hidenavigation 1 amp theme dark

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Using  Underscore js or lodash js    intersection   0 345 324     1 0 324        gives  0 324

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Another indexed approach able to process any number of arrays at once      Calculate intersection of multiple array or object values  function intersect  arrList        var arrLength   Object keys arrList  length              Also accepts regular objects as input      var index           for  var i in arrList            for  var j in arrList i                 var v   arrList i  j               if  index v      undefined  index v    0              index v                           var retv           for  var i in index            if  index i     arrLength  retv push i              return retv       It works only for values that can be evaluated as strings and you should pass them as an array like   intersect   arr1  arr2  arr3            but it transparently accepts objects as parameter or as any of the elements to be intersected  always returning array of common values   Examples   intersect   foo   1  2  3  4   bar   a  2  j 4         2  4  intersect    x   hello   y   world      hello    user           hello     EDIT  I just noticed that this is  in a way  slightly buggy   That is  I coded it thinking that input arrays cannot itself contain repetitions  as provided example doesn t    But if input arrays happen to contain repetitions  that would produce wrong results  Example  using below implementation    intersect    1  3  4  6  3    1  8  99        Expected     1       Actual     1    3      Fortunately this is easy to fix by simply adding second level indexing  That is   Change           if  index v      undefined  index v    0          index v       by           if  index v      undefined  index v                index v  i    true     Mark as present in i input       and            if  index i     arrLength  retv push i     by            if  Object keys index i   length    arrLength  retv push i     Complete example      Calculate intersection of multiple array or object values  function intersect  arrList        var arrLength   Object keys arrList  length              Also accepts regular objects as input      var index           for  var i in arrList            for  var j in arrList i                 var v   arrList i  j               if  index v      undefined  index v                    index v  i    true     Mark as present in i input                        var retv           for  var i in index            if  Object keys index i   length    arrLength  retv push i              return retv      intersect    1  3  4  6  3    1  8  99           1

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How about just using associative arrays   function intersect a  b        var d1           var d2           var results           for  var i   0  i  lt  a length  i              d1 a i     true            for  var j   0  j  lt  b length  j              d2 b j     true            for  var k in d1            if  d2 k                results push k             return results      edit      new version function intersect a  b        var d           var results           for  var i   0  i  lt  b length  i              d b i     true            for  var j   0  j  lt  a length  j              if  d a j                 results push a j              return results

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With some restrictions on your data  you can do it in linear time   For positive integers  use an array mapping the values to a  seen not seen  boolean   function intersectIntegers array1 array2        var seen            result        for  var i   0  i  lt  array1 length  i           seen array1 i     true          for  var i   0  i  lt  array2 length  i           if   seen array2 i            result push array2 i            return result      There is a similar technique for objects  take a dummy key  set it to  true  for each element in array1  then look for this key in elements of array2  Clean up when you re done   function intersectObjects array1 array2        var result        var key  tmpKey intersect     for  var i   0  i  lt  array1 length  i           array1 i  key    true          for  var i   0  i  lt  array2 length  i           if  array2 i  key           result push array2 i            for  var i   0  i  lt  array1 length  i           delete array1 i  key           return result      Of course you need to be sure the key didn t appear before  otherwise you ll be destroying your data

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The performance of  atk s implementation for sorted arrays of primitives can be improved by using  pop rather than  shift   function intersect array1  array2       var result             Don t destroy the original arrays    var a   array1 slice 0      var b   array2 slice 0      var aLast   a length - 1     var bLast   b length - 1     while  aLast  gt   0  amp  amp  bLast  gt   0          if  a aLast   gt  b bLast               a pop             aLast--          else if  a aLast   lt  b bLast              b pop             bLast--          else    they re equal               result push a pop              b pop             aLast--           bLast--                  return result      I created a benchmark using jsPerf  http   bit ly P9FrZK   It s about three times faster to use  pop

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A functional approach with ES2015  A functional approach must consider using only pure functions without side effects  each of which is only concerned with a single job   These restrictions enhance the composability and reusability of the functions involved    x000D   x000D     small  reusable auxiliary functions x000D   x000D  const createSet   xs   gt  new Set xs   x000D  const filter   f   gt  xs   gt  xs filter apply f    x000D  const apply   f   gt  x   gt  f x   x000D   x000D   x000D     intersection x000D   x000D  const intersect   xs   gt  ys   gt    x000D    const zs   createSet ys   x000D    return filter x   gt  zs has x  x000D         true x000D         false x000D       xs   x000D     x000D   x000D   x000D     mock data x000D   x000D  const xs    1 2 2 3 4 5   x000D  const ys    0 1 2 3 3 3 6 7 8 9   x000D   x000D   x000D     run it x000D   x000D  console log  intersect xs   ys     x000D   x000D   x000D    Please note that the native Set type is used  which has an advantageous lookup performance   Avoid duplicates  Obviously repeatedly occurring items from the first Array are preserved  while the second Array is de-duplicated  This may be or may be not the desired behavior  If you need a unique result just apply dedupe to the first argument    x000D   x000D     auxiliary functions x000D   x000D  const apply   f   gt  x   gt  f x   x000D  const comp   f   gt  g   gt  x   gt  f g x    x000D  const afrom   apply Array from   x000D  const createSet   xs   gt  new Set xs   x000D  const filter   f   gt  xs   gt  xs filter apply f    x000D   x000D   x000D     intersection x000D   x000D  const intersect   xs   gt  ys   gt    x000D    const zs   createSet ys   x000D    return filter x   gt  zs has x  x000D         true x000D         false x000D       xs   x000D     x000D   x000D   x000D     de-duplication x000D   x000D  const dedupe   comp afrom   createSet   x000D   x000D   x000D     mock data x000D   x000D  const xs    1 2 2 3 4 5   x000D  const ys    0 1 2 3 3 3 6 7 8 9   x000D   x000D   x000D     unique result x000D   x000D  console log  intersect dedupe xs    ys     x000D   x000D   x000D    Compute the intersection of any number of Arrays  If you want to compute the intersection of an arbitrarily number of Arrays just compose intersect with foldl  Here is a convenience function    x000D   x000D     auxiliary functions x000D   x000D  const apply   f   gt  x   gt  f x   x000D  const uncurry   f   gt   x  y    gt  f x   y   x000D  const createSet   xs   gt  new Set xs   x000D  const filter   f   gt  xs   gt  xs filter apply f    x000D  const foldl   f   gt  acc   gt  xs   gt  xs reduce uncurry f   acc   x000D   x000D   x000D     intersection x000D   x000D  const intersect   xs   gt  ys   gt    x000D    const zs   createSet ys   x000D    return filter x   gt  zs has x  x000D         true x000D         false x000D       xs   x000D     x000D   x000D   x000D     intersection of an arbitrarily number of Arrays x000D   x000D  const intersectn    head     tail    gt  foldl intersect   head   tail   x000D   x000D   x000D     mock data x000D   x000D  const xs    1 2 2 3 4 5   x000D  const ys    0 1 2 3 3 3 6 7 8 9   x000D  const zs    0 1 2 3 4 5 6   x000D   x000D   x000D     run x000D   x000D  console log  intersectn xs  ys  zs     x000D   x000D   x000D

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not about efficiency  but easy to follow  here is an example of unions and intersections of sets  it handles arrays of sets and sets of sets   http   jsfiddle net zhulien NF68T      process array  element  element      if allow abort ignore the result function processArray arr a  cb a  blnAllowAbort a        var arrResult           var blnAborted   false      var intI   0       while   intI  lt  arr a length   amp  amp   blnAborted     false                 if  blnAllowAbort a                        blnAborted   cb a arr a intI                      else                       arrResult intI    cb a arr a intI                      intI               return arrResult        process array of operations  operation arguments     function processOperations arrOperations a        var arrResult           var fnOperationE       for var intI   0  intR   0  intI  lt  arrOperations a length  intI  2  intR                   var fnOperation   arrOperations a intI 0           var fnArgs   arrOperations a intI 1           if  fnArgs     undefined                        arrResult intR    fnOperation                      else                       arrResult intR    fnOperation fnArgs                        return arrResult        return whether an element exists in an array function find arr a  varElement a        var blnResult   false       processArray arr a  function varToMatch a                var blnAbort   false           if  varToMatch a     varElement a                        blnResult   true              blnAbort   true                     return blnAbort         true        return blnResult        return the union of all sets function union arr a        var arrResult           var intI   0       processArray arr a  function arrSet a                processArray arrSet a  function varElement a                           if the element doesn t exist in our result             if  find arrResult  varElement a      false                                   add it                 arrResult intI    varElement a                  intI                                           return arrResult        return the intersection of all sets function intersection arr a        var arrResult           var intI   0          for each set     processArray arr a  function arrSet a                   every number is a candidate         processArray arrSet a  function varCandidate a                        var blnCandidate   true                  for each set             processArray arr a  function arrSet a                                   check that the candidate exists                 var blnFoundPart   find arrSet a  varCandidate a                       if the candidate does not exist                 if  blnFoundPart     false                                           no longer a candidate                     blnCandidate   false                                                 if  blnCandidate                                   if the candidate doesn t exist in our result                 if  find arrResult  varCandidate a      false                                           add it                     arrResult intI    varCandidate a                      intI                                                             return arrResult     var strOutput       var arrSet1    1 2 3   var arrSet2    2 5 6   var arrSet3    7 8 9 2       return the union of the sets strOutput   union  arrSet1  arrSet2  arrSet3    alert strOutput       return the intersection of 3 sets strOutput   intersection  arrSet1  arrSet2  arrSet3    alert strOutput       of 3 sets of sets  which set is the intersecting set strOutput   processOperations  intersection   arrSet1  arrSet2    arrSet2    arrSet2  arrSet3      alert strOutput

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function intersectionOfArrays arr1  arr2        return arr1 filter  element    gt  arr2 indexOf element      -1  filter  element  pos  self    gt  self indexOf element     pos

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This is probably the simplest one  besides list1 filter n    list2 includes n     x000D   x000D  var list1     bread    ice cream    cereals    strawberry    chocolate   x000D  var list2     bread    cherry    ice cream    oats   x000D   x000D  function check common list1  list2   x000D    x000D   list3      x000D   for  let i 0  i lt list1 length  i     x000D     x000D    for  let j 0  j lt list2 length  j      x000D     if  list1 i      list2 j    x000D      list3 push list1 i        x000D         x000D      x000D     x000D     x000D   return list3 x000D    x000D    x000D   x000D  check common list1  list2       bread    ice cream   x000D   x000D   x000D

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intersection of N arrays in coffeescript  getIntersection   arrays  - gt      if not arrays length         return        a1   arrays 0      for a2 in arrays slice 1          a    val for val in a1 when val in a2          a1   a     return a1 unique

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x000D   x000D  var arrays     x000D       1  2  3   x000D       2  3  4  5  x000D    x000D  function commonValue     arr    x000D      let res   arr 0  filter function  x    x000D          return arr every  y    gt  y includes x   x000D         x000D      return res  x000D    x000D  commonValue    arrays   x000D   x000D   x000D

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I extended tarulen s answer to work with any number of arrays  It also should work with non-integer values   function intersect          const last   arguments length - 1      var seen         var result         for  var i   0  i  lt  last  i                for  var j   0  j  lt  arguments i  length  j                   if  seen arguments i  j                       seen arguments i  j      1                            else if   i                       seen arguments i  j     1                                    for  var i   0  i  lt  arguments last  length  i              if   seen arguments last  i       last              result push arguments last  i                  return result

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Create an Object using one array and loop through the second array to check if the value exists as key   function intersection arr1  arr2      var myObj         var myArr         for  var i   0  len   arr1 length  i  lt  len  i    1        if myObj arr1 i            myObj arr1 i      1         else         myObj arr1 i     1              for  var j   0  len   arr2 length  j  lt  len  j    1        if myObj arr2 j    amp  amp  myArr indexOf arr2 j       -1          myArr push arr2 j                return myArr

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Destructive seems simplest  especially if we can assume the input is sorted      destructively finds the intersection of     two arrays in a simple fashion          PARAMS     a - first array  must already be sorted     b - second array  must already be sorted       NOTES     State of input arrays is undefined when     the function returns   They should be       prolly  be dumped         Should have O n  operations  where n is        n   MIN a length  b length      function intersection destructive a  b      var result         while  a length  gt  0  amp  amp  b length  gt  0              if       a 0   lt  b 0     a shift           else if  a 0   gt  b 0     b shift           else    they re equal                  result push a shift            b shift                  return result      Non-destructive has to be a hair more complicated  since we   ve got to track indices      finds the intersection of     two arrays in a simple fashion          PARAMS     a - first array  must already be sorted     b - second array  must already be sorted       NOTES        Should have O n  operations  where n is        n   MIN a length    b length        function intersect safe a  b      var ai 0  bi 0    var result          while  ai  lt  a length  amp  amp  bi  lt  b length            if       a ai   lt  b bi     ai           else if  a ai   gt  b bi     bi           else    they re equal                  result push a ai           ai           bi                  return result

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A tiny tweak to the smallest one here  the filter indexOf solution   namely creating an index of the values in one of the arrays using a JavaScript object  will reduce it from O N M  to  probably  linear time  source1 source2  function intersect a  b      var aa         a forEach function v    aa v  1        return b filter function v    return v in aa          This isn t the very simplest solution  it s more code than filter indexOf   nor is it the very fastest  probably slower by a constant factor than intersect safe     but seems like a pretty good balance  It is on the very simple side  while providing good performance  and it doesn t require pre-sorted inputs

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I have written an intesection function which can even detect intersection of array of objects based on particular property of those objects   For instance   if arr1     id  10    id  20   and arr2      id  20    id  25     and we want intersection based on the id property  then the output should be       id  20     As such  the function for the same  note  ES6 code  is    const intersect    arr1  arr2  accessors    v   gt  v  v   gt  v     gt        const  fn1  fn2    accessors      const set   new Set arr2 map v   gt  fn2 v         return arr1 filter value   gt  set has fn1 value          and you can call the function as   intersect arr1  arr2   elem   gt  elem id  elem   gt  elem id     Also note  this function finds intersection considering the first array is the primary array and thus the intersection result will be that of the primary array

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Building on Anon s excellent answer  this one returns the intersection of two or more arrays   function arrayIntersect arrayOfArrays                var arrayCopy   arrayOfArrays slice            baseArray   arrayCopy pop         return baseArray filter function item            return arrayCopy every function itemList                return itemList indexOf item      -1

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I ll contribute with what has been working out best for me   if   Array prototype intersect   Array prototype intersect   function  arr1         var r       o       l   this length  i  v      for  i   0  i  lt  l  i              o this i     true            l   arr1 length      for  i   0  i  lt  l  i              v   arr1 i           if  v in o                r push v                       return r

[javascript] Simplest code for array intersection in javascript

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