Merge two array of objects based on a key

Question

I have two arrays    Array 1         id   abdc4051   date   2017-01-24          id   abdc4052   date   2017-01-22        and array 2         id   abdc4051   name   ab         id   abdc4052   name   abc        I need to merge these two arrays based on id and get this         id   abdc4051   date   2017-01-24   name   ab         id   abdc4052   date   2017-01-22   name   abc        How can I do this without iterating trough Object keys

User · Answer

I was able to achieve this with a nested mapping of the two arrays and updating the initial array   member map mem   gt    return memberInfo map info   gt        if  info id     mem userId            mem date   info date          return mem

User · Answer

You could use an arbitrary count of arrays and map on the same index new objects    x000D   x000D  var array1      id   abdc4051   date   2017-01-24       id   abdc4052   date   2017-01-22      x000D      array2      id   abdc4051   name   ab       id   abdc4052   name   abc      x000D      result    array1  array2  reduce  a  b    gt  a map  c  i    gt  Object assign     c  b i      x000D       x000D  console log result   x000D   as-console-wrapper   max-height  100   important  top  0    x000D   x000D   x000D

User · Answer

To merge the two arrays on id  assuming the arrays are equal length   arr1 map item   gt            item         arr2 find    id      gt  id     item id

User · Answer

Well    assuming both arrays are of the same length  I would probably do something like this   var newArr      for  var i   0  i  lt  array1 length  i         if  array1 i  id     array2 i  id          newArr push  id  array1 i  id  date  array1 i  date  name  array2 i  name

User · Answer

We can use lodash here    merge works as you expected  It works with the common key present    merge array1  array2

User · Answer

You can do it like this -   x000D   x000D  let arr1     x000D        id   abdc4051   date   2017-01-24     x000D        id   abdc4052   date   2017-01-22    x000D     x000D   x000D  let arr2     x000D        id   abdc4051   name   ab     x000D        id   abdc4052   name   abc    x000D     x000D   x000D  let arr3   arr1 map  item  i    gt  Object assign     item  arr2 i     x000D   x000D  console log arr3   x000D   x000D   x000D      Use below code if arr1 and arr2 are in a different order    x000D   x000D  let arr1     x000D      id   abdc4051   date   2017-01-24      x000D      id   abdc4052   date   2017-01-22    x000D     x000D   x000D  let arr2     x000D      id   abdc4051   name   ab     x000D      id   abdc4052   name   abc    x000D     x000D   x000D  let merged       x000D   x000D  for let i 0  i lt arr1 length  i      x000D    merged push   x000D        arr1 i    x000D         arr2 find  itmInner    gt  itmInner id     arr1 i  id    x000D       x000D    x000D   x000D  console log merged   x000D   x000D   x000D    Use this if arr1 and arr2 are in a same order   x000D   x000D  let arr1     x000D      id   abdc4051   date   2017-01-24      x000D      id   abdc4052   date   2017-01-22    x000D     x000D   x000D  let arr2     x000D      id   abdc4051   name   ab     x000D      id   abdc4052   name   abc    x000D     x000D   x000D  let merged       x000D   x000D  for let i 0  i lt arr1 length  i      x000D    merged push   x000D        arr1 i    x000D        arr2 i  x000D        x000D    x000D   x000D  console log merged   x000D   x000D   x000D

User · Answer

You can recursively merge them into one as follows    x000D   x000D  function mergeRecursive obj1  obj2    x000D      for  var p in obj2    x000D          try   x000D                 Property in destination object set  update its value  x000D              if  obj2 p  constructor    Object    x000D                  obj1 p    this mergeRecursive obj1 p   obj2 p    x000D   x000D                else   x000D                  obj1 p    obj2 p   x000D   x000D                x000D   x000D            catch  e    x000D              obj1 p    obj2 p   x000D   x000D            x000D        x000D      return obj1  x000D    x000D   x000D  arr1     x000D        id   abdc4051   date   2017-01-24     x000D        id   abdc4052   date   2017-01-22    x000D     x000D  arr2     x000D        id   abdc4051   name   ab     x000D        id   abdc4052   name   abc    x000D     x000D   x000D  mergeRecursive arr1  arr2  x000D  console log JSON stringify arr1   x000D   x000D   x000D

User · Answer

You can use array methods  x000D   x000D  let arrayA   x000D   id   abdc4051   date   2017-01-24    x000D   id   abdc4052   date   2017-01-22    x000D   x000D  let arrayB   x000D   id   abdc4051   name   ab    x000D   id   abdc4052   name   abc    x000D   x000D  let arrayC       x000D   x000D   x000D  function isBiggerThan10 element  index  array    x000D    return element  gt  10  x000D    x000D   x000D  arrayA forEach function element   x000D    arrayC push   x000D    id element id  x000D    date element date  x000D    name  arrayB find e  gt e id   element id   name x000D          x000D      x000D   x000D  console log arrayC   x000D   x000D    0  id   abdc4051   date   2017-01-24   name   ab   x000D    1  id   abdc4052   date   2017-01-22   name   abc   x000D   x000D   x000D

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This is a version when you have an object and an array and you want to merge them and give the array a key value so it fits into the object nicely    x000D   x000D  var fileData     x000D         id     1    filename     myfile1    score    33 1     x000D         id     2    filename     myfile2    score    31 4     x000D         id     3    filename     myfile3    score    36 3     x000D         id     4    filename     myfile4    score    23 9   x000D     x000D   x000D  var fileQuality    0 23456543 0 13413131 0 1941344 0 7854522   x000D   x000D  var newOjbect   fileData map  item  i    gt  Object assign     item   fileQuality fileQuality i      x000D   x000D  console log newOjbect   x000D   x000D   x000D

User · Answer

Non of these solutions worked for my case    missing objects can exist in either array runtime complexity of O n    notes    I used lodash but it s easy to replace with something else Also used Typescript  just remove ignore the types    import   keyBy  values   from  lodash    interface IStringTMap lt T gt       key  string   T     type IIdentified       id   string   number      export function mergeArrayById lt T extends IIdentified gt     array1  T      array2  T      T       const mergedObjectMap  IStringTMap lt T gt    keyBy array1   id       const finalArray  T            for  const object of array2        if  object id  amp  amp  mergedObjectMap object id           mergedObjectMap object id                 mergedObjectMap object id              object                 else         finalArray push object                values mergedObjectMap  forEach object   gt        finalArray push object            return finalArray

User · Answer

Here s an O n  solution using reduce and Object assign  const joinById        lists     gt      Object values          lists reduce                idx  list     gt                    list forEach    recod     gt                        if  idx  recod id                             idx  recod id     Object assign  idx  recod id    recod                       else                         idx  recod id     recod                                     return idx                                                 Each list gets reduced to a single object where the keys are ids and the values are the objects  If there s a value at the given key already  it gets object assign called on it and the current record   Here s the generic O n m  solution  where n is the number of records and m is the number of keys  This will only work for valid object keys  You can convert any value to base64 and use that if you need to   const join     keys     lists     gt      lists reduce            res  list     gt                list forEach    record     gt                    let hasNode   keys reduce                        idx  key     gt  idx  amp  amp  idx  record  key                          res  0   tree                                   if  hasNode                         const i   hasNode i                     Object assign  res  i   value  record                       res  i   found                     else                       let node   keys reduce    idx  key     gt                            if  idx  record  key                                   return idx  record  key                             else                             idx  record  key                                  return idx  record  key                            res  0   tree                       node i   res  0   i                       res  node i                               found  1                          value  record                                                                     return res                        i  1  tree                              slice  1             filter  node   gt  node found     lists length             map  n   gt  n value     This is essentially the same as the joinById method  except that it keeps an index object to identify records to join  The records are stored in an array and the index stores the position of the record for the given key set and the number of lists it s been found in   Each time the same key set is encountered  the node is found in the tree  the element at it s index is updated  and the number of times it s been found is incremented   finally  the idx object is removed from the array with the slice  any elements that weren t found in each set are removed  This makes it an inner join  you could remove this filter and have a full outer join   finally each element is mapped to it s value  and you have the merged array

User · Answer

If you have 2 arrays need to be merged based on values even its in different order  let arr1           id  1   value  this   other   that           id  2   value  this   other   that        let arr2           id  2   key  val2          id  1   key  val1        you can do like this   const result   arr1 map item   gt        const obj   arr2 find o   gt  o id     item id       return      item     obj           console log result

User · Answer

This solution is applicable even when you have different size of array being merged  Also  even if the keys on which match is happening has a different name   const arr1         id   abdc4051   date   2017-01-24          id   abdc4052   date   2017-01-22         id   abdc4053   date   2017-01-22       const arr2         nameId   abdc4051   name   ab         nameId   abdc4052   name   abc         Now to merge these use a Map as follows   const map   new Map    arr1 forEach item   gt  map set item id  item    arr2 forEach item   gt  map set item nameId      map get item nameId      item     const mergedArr   Array from map values       This should result in              id    abdc4051        date    2017-01-24        nameId    abdc4051        name    ab                id    abdc4052        date    2017-01-22        nameId    abdc4052        name    abc                id    abdc4053        date    2017-01-22

User · Answer

You can do this in one line   x000D   x000D  let arr1     x000D        id   abdc4051   date   2017-01-24     x000D        id   abdc4052   date   2017-01-22    x000D     x000D   x000D  let arr2     x000D        id   abdc4051   name   ab     x000D        id   abdc4052   name   abc    x000D     x000D   x000D  const mergeById    a1  a2    gt  x000D      a1 map itm   gt     x000D             a2 find  item    gt   item id     itm id   amp  amp  item   x000D             itm x000D           x000D   x000D  console log mergeById arr1  arr2    x000D   x000D   x000D     Map over array1 Search through array2 for array1 id If you find it    spread the result of array2 into array1   The final array will only contain id s that match from both arrays

[javascript] Merge two array of objects based on a key

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