How can I find matching values in two arrays

Question

I have two arrays  and I want to be able to compare the two and only return the values that match  For example both arrays have the value cat so that is what will be returned  I haven t found anything like this  What would be the best way to return similarities    var array1     cat    sum   fun    run    var array2     bat    cat   dog   sun    hut    gut       if value in array1 is equal to value in array2 then return match  cat

User · Answer

Libraries like underscore and lodash have a utility method called intersection to find matches in arrays passed in  Take a look at  http   underscorejs org  intersection

User · Answer

Loop through the second array each time you iterate over an element in the first array  then check for matches   var array1     cat    sum    fun    run        array2     bat    cat    dog    sun    hut    gut     function getMatch a  b        var matches            for   var i   0  i  lt  a length  i               for   var e   0  e  lt  b length  e                   if   a i      b e    matches push  a i                         return matches     getMatch array1  array2        cat

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If your values are non-null strings or numbers  you can use an object as a dictionary   var map       result       i  for  i   0  i  lt  array1 length    i        map array1 i     1     for  i   0  i  lt  array2 length    i        if  map array2 i       1            result push array2 i                avoid returning a value twice if it appears twice in array 2         map array2 i     0           return result

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Done as a answer so I can do formatting     This is the the process you need to go through   Looping through an array for the specifics   create an empty array loop through array1  element by element      loop through array2  element by element       if array1 element    array2 element         add to your new array

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This function runs in O n log n    m log m   compared to O n m   as seen in the other solutions with loops indexOf  which can be useful if you are dealing with lots of values   However  because neither  a   gt  1 nor  a   lt  1  this only works for elements of the same type   function intersect arrays a  b        var sorted a   a concat   sort        var sorted b   b concat   sort        var common           var a i   0      var b i   0       while  a i  lt  a length             amp  amp  b i  lt  b length                if  sorted a a i      sorted b b i                 common push sorted a a i                a i                b i                      else if sorted a a i   lt  sorted b b i                 a i                      else               b i                        return common      Example   var array1     cat    sum    fun    hut      modified for additional match     array2     bat    cat    dog    sun    hut    gut    intersect arrays array1  array2    gt  gt    cat    hut

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I found a slight alteration on what  jota3 suggested worked perfectly for me   var intersections   array1 filter e   gt  array2 indexOf e      -1     Hope this helps

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Naturally  my approach was to loop through the first array once and check the index of each value in the second array  If the index is  gt  -1  then push it onto the returned array    Array prototype diff   function arr2        var ret           for var i in this               if arr2 indexOf this i    gt  -1               ret push this i                        return ret         My solution doesn t use two loops like others do so it may run a bit faster  If you want to avoid using for  in  you can sort both arrays first to reindex all their values   Array prototype diff   function arr2        var ret           this sort        arr2 sort        for var i   0  i  lt  this length  i    1            if arr2 indexOf this i    gt  -1               ret push this i                        return ret       Usage would look like   var array1     cat    sum   fun    run    hut    var array2     bat    cat   dog   sun    hut    gut     console log array1 diff array2      If you have an issue problem with extending the Array prototype  you could easily change this to a function   var diff   function arr  arr2      And you d change anywhere where the func originally said this to arr2

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Iterate on  array1 and find the indexof element present in array2   var array1     cat    sum   fun    run    var array2     bat    cat   sun    hut    gut    var str     for var i 0 i lt array1 length i             if array2 indexOf array1 i      -1              str  array1 i                       console log str

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You can use javascript function  find   As it says in MDN  it will return the first value that is true  If such an element is found  find immediately returns the value of that element  Otherwise  find returns undefined    x000D   x000D  var array1     cat    sum   fun    run    x000D  var array2     bat    cat   dog   sun    hut    gut    x000D   x000D  found   array1 find  val   gt  array2 includes val    x000D  console log found  x000D   x000D   x000D

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You can use     const intersection   array1 filter element   gt  array2 includes element

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use lodash   GLOBAL utils   require  lodash   var arr1     first     second    var arr2     second      var result   utils difference arr1   arr2   console log    result      result

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var array1     1  2  3  4  5  6   var array2    1  2  3  4  5  6  7  8  9   var array3   array2 filter function obj         return array1 indexOf obj     -1

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With some ES6   let sortedArray       firstArr map  first    gt      sortedArray defaultArray findIndex def   gt  def     first     first      sortedArray   sortedArray filter v   gt  v     This snippet also sorts the firstArr based on the order of the defaultArray  like    let firstArr     apple    kiwi    banana    let defaultArray     kiwi    apple    pear        console log sortedArray        kiwi    apple

[javascript] How can I find matching values in two arrays?

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