How to Flatten a Multidimensional Array

Question

Is it possible  in PHP  to flatten a  bi multi dimensional array without using recursion or references   I m only interested in the values so the keys can be ignored  I m thinking in the lines of array map   and array values

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Try the following simple function   function  flatten array  arr      while   arr        list  key   value    each  arr        is array  value     arr    value    out  key     value      unset  arr  key          return  array  out      So from this   array      und    gt     array        profiles    gt       array         0   gt         array            commerce customer address    gt           array              und    gt             array               0   gt               array                  first name    gt   First name                  last name    gt   Last name                  thoroughfare    gt   Address 1                  premise    gt   Address 2                  locality    gt   Town City                  administrative area    gt   County                  postal code    gt   Postcode                                                                   you get   array      first name    gt   First name      last name    gt   Last name      thoroughfare    gt   Address 1      premise    gt   Address 2      locality    gt   Town City      administrative area    gt   County      postal code    gt   Postcode

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Flattens two dimensional arrays only    arr    1  2   3  4     arr   array reduce  arr  function   a   b         return array merge  a   array   b               Result   1  2  3  4

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Solution for 2 dimensional array  Please try this      array    your array   result   call user func array  array merge    array    echo   lt pre gt    print r  result     EDIT   21-Aug-13  Here is the solution which works for multi-dimensional array    function array flatten  array         return   array        foreach   array as  key   gt   value            if  is array  value                 return   array merge  return  array flatten  value              else                return  key     value                       return  return      array    Your array   result   array flatten  array    echo   lt pre gt    print r  result     Ref  http   php net manual en function call-user-func-array php

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If you really don t like a recursion     try shifting instead      a   array 1 2 array 3 4  array 5 6 7   8   9    o       for   i 0   i lt count  a    i          if  is array  a  i              array splice  a   i 1  0   a  i          else            o      a  i             Note  In this simple version  this does not support array keys

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If you have an array of objects and want to flatten it with a node  just use this function   function objectArray flatten  array  childField         result   array        foreach   array as  node                 result      node          if isset  node- gt  childField                          result   array merge                   result                   objectArray flatten  node- gt  childField  childField                             unset  node- gt  childField                        return  result

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This solution is non-recursive  Note that the order of the elements will be somewhat mixed   function flatten  array         return   array        while count  array              value   array shift  array           if is array  value               foreach  value as  sub                   array      sub          else              return      value            return  return

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This can be achieved by using array walk recursive   a   array 1 2 array 3 4  array 5 6 7   8   9   array walk recursive  a  function  v  use   amp  r   r    v     print r  r     Working example  - https   3v4l org FpIrG

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I believe this is the cleanest solution without using any mutations nor unfamiliar classes    lt  php  function flatten  array        return array reduce  array  function  acc   item           return array merge  acc  is array  item    flatten  item      item                       usage  array    1  2   3  4    5   6  7    8  9  10   print r flatten  array

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For merging values of a multidimensional array into one         array            0   gt               0   gt   a1              1   gt   b1              2   gt   c1              3   gt   d1                   1   gt               0   gt   a2              1   gt   b2              2   gt   c2                        becomes           array            0   gt   a1          1   gt   b1          2   gt   c1          3   gt   d1          4   gt   a2          5   gt   b2          6   gt   c2                    array reduce        multiArray       function   lastItem   currentItem             lastItem    lastItem    array            return array merge  lastItem  array values  currentItem               Gist snippet

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If you want to keep also your keys that is solution  function flatten array  array         return   array        array walk recursive  array  function  value   key  use   amp  return     return  key     value          return  return     Unfortunately it outputs only final nested arrays  without middle keys  So for the following example   array   array       sweet    gt  array           a    gt   apple            b    gt   banana         sour    gt   lemon     print r flatten  fruits     Output is  Array        a    gt  apple      b    gt  banana      sour    gt  lemon

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Here s a simplistic approach    My Array   array 1 2 array 3 4  array 5 6 7   8   9    function checkArray  value        foreach   value as  var            if   is array  var                  checkArray  var             else               echo  var                     checkArray  My Array

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Uses recursion   Hopefully upon seeing how not-complex it is  your fear of recursion will dissipate once you see how not-complex it is   function flatten  array        if   is array  array                nothing to do if it s not an array         return array  array               result   array        foreach   array as  value               explode the sub-array  and add the parts          result   array merge  result  flatten  value               return  result       arr   array  foo   array  nobody    expects   array  another    level     the    Spanish    Inquisition     bar    echo   lt ul gt    foreach  flatten  arr  as  value        echo   lt li gt     value    lt  li gt      echo   lt ul gt      Output    lt ul gt  lt li gt foo lt  li gt  lt li gt nobody lt  li gt  lt li gt expects lt  li gt  lt li gt another lt  li gt  lt li gt level lt  li gt  lt li gt the lt  li gt  lt li gt Spanish lt  li gt  lt li gt Inquisition lt  li gt  lt li gt bar lt  li gt  lt ul gt

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The trick is passing the both the source and destination arrays by reference   function flatten array  amp  arr   amp  dst        if  isset  dst      is array  dst              dst   array              if  is array  arr              dst      arr        else           foreach  arr as  amp  subject                flatten array  subject   dst                       recursive   array  1   array  2   3  array  4  array  5   6     7  array array array  8    9    10      echo  Recursive   r n   print r  recursive    flat   null  flatten array  recursive   flat    echo  Flat   r n   print r  flat       If you change line 3 to  dst      amp  arr    you won t waste memory     since all you re doing is copying references  and imploding the array     into a string will be both memory efficient and fast    echo  String  r n   echo implode      flat

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How about using a recursive generator  https   ideone com d0TXCg   lt  php   array          name    gt   Allen Linatoc        profile    gt             age    gt  21           favourite games    gt     Call of Duty    Titanfall    Far Cry              foreach  iterate  array  as  item        var dump  item       function iterate  array        foreach   array as  item            if  is array  item                 yield from iterate  item             else               yield  item

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This version can do deep  shallow  or a specific number of levels           param  array object  array  array of mixed values to flatten     param  int boolean   level  0 deep  1 shallow  2 2 levels  3        return array     function flatten  array   level   0         level    int   level       result   array        foreach   array as  i   gt   v            if  0  lt    level  amp  amp  is array  v                  v   flatten  v   level  gt  1    level - 1   0 -  level                result   array merge  result   v             elseif  is int  i                  result      v            else                result  i     v                       return  result

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Anyone looking for a really clean solution to this  here s an option     test array   array      array  test    gt  0  0  0  0       array 0  0   merp    gt  array  herp    gt   derp    0       array 0  0  0  0       array 0  0  0  0      it   new RecursiveIteratorIterator new RecursiveArrayIterator  test array    var dump  iterator to array  it  false         Prints    0 0 0 0 0 0 derp 0 0 0 0 0 0 0 0 0

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I needed to represent PHP multidimensional array in HTML input format    test          a    gt             b    gt                 c    gt    a    b                         b    gt   c        c    gt             d    gt   e             flatten   function   input   parent       use   amp  flatten         return            foreach   input as  k   gt   v            if  is array  v                  return   array merge  return   flatten  v  array merge  parent    k                else               if   parent                     key   implode        parent            k                         if  substr count  key          substr count  key                               key   preg replace              key  1                                   else                    key    k                                         return  key     v                       return  return      die var dump   flatten  test       array 4        a b  c  0     gt    string 1   a      a b  c  1     gt    string 1   b      b    gt    string 1   c      c d     gt    string 1   e

User · Answer

As of PHP 5 3 the shortest solution seems to be array walk recursive   with the new closures syntax   function flatten array  array         return   array        array walk recursive  array  function  a  use   amp  return     return      a          return  return

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Straightforward and One-liner answer   function flatten array array  array        return iterator to array           new  RecursiveIteratorIterator new  RecursiveArrayIterator  array         Usage    array          name    gt   Allen Linatoc        profile    gt             age    gt  21           favourite games    gt     Call of Duty    Titanfall    Far Cry              print r  flatten array  array       Output  in PsySH    Array        name    gt  Allen Linatoc      age    gt  21      0    gt  Call of Duty      1    gt  Titanfall      2    gt  Far Cry     Now it s pretty up to you now how you ll handle the keys  Cheers    EDIT  2017-03-01   Quoting Nigel Alderton s concern issue      Just to clarify  this preserves keys  even numeric ones  so values that have the same key are lost  For example  array     a    b   c    becomes Array   0    gt  b   1    gt  c    The  a  is lost because  b  also has a key of 0   Quoting Svish s answer      Just add false as second parameter   use keys  to the iterator to array call

User · Answer

To flatten w o recursion  as you have asked for   you can use a stack  Naturally you can put this into a function of it s own like array flatten  The following is a version that works w o keys   function array flatten array  array         flat   array       initialize return array      stack   array values  array      initialize stack     while  stack     process stack until done                value   array shift  stack           if  is array  value      a value to further process                       array unshift  stack      value                     else    a value to take                        flat      value                      return  flat     Elements are processed in their order  Because subelements will be moved on top of the stack  they will be processed next  It s possible to take keys into account as well  however  you ll need a different strategy to handle the stack  That s needed because you need to deal with possible duplicate keys in the sub-arrays  A similar answer in a related question  PHP Walk through multidimensional array while preserving keys I m not specifically sure  but I I had tested this in the past  The RecurisiveIterator does use recursion  so it depends on what you really need  Should be possible to create a recursive iterator based on stacks as well  foreach new FlatRecursiveArrayIterator  array  as  key   gt   value        echo  quot      key   value n quot      Demo I didn t make it so far  to implement the stack based on RecursiveIterator which I think is a nice idea

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This is my solution  using a reference   function arrayFlatten  array in   amp  array out        if is array  array in            foreach   array in as  element                  arrayFlatten  element   array out                       else           array out      array in             arr1   array  1    2   array array array  3     4    5     array array  6       arrayFlatten  arr1   arr2    echo   lt pre gt    print r  arr2   echo   lt  pre gt

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You can use the Standard PHP Library  SPL  to  hide  the recursion    a   array 1 2 array 3 4  array 5 6 7   8   9    it   new RecursiveIteratorIterator new RecursiveArrayIterator  a    foreach  it as  v      echo  v           prints  1 2 3 4 5 6 7 8 9

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You can do it with ouzo goodies     result   Arrays  flatten  multidimensional     See  Here

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Just posting a some else solution   function flatMultidimensionalArray array  amp   arr   array        result            array walk recursive   arr  static function   amp  value   amp  key  use   amp  result             result  key     value               return  result

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lt  php   recursive solution    test array  nested array     1 2  3   4  5     6  7  gt  7 8 9 10           ----------------------------------------- function call and return result to an array ------------------------------------------    index count   1   flatered array   array     flatered array   flat array  nested array   index count      ----------------------------------------- Print Result -----------------------------------------   echo   lt pre gt    print r  flatered array       ----------------------------------------- function to flaten an array  -----------------------------------------   function flat array  nested array   amp   index count   amp   flatered array       foreach  nested array AS  key  gt  val          if is array  val             flat array  val   index count   flatered array                 else            flatered array  index count     val             index count                     return  flatered array      gt

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For php 5 2  function flatten array  array         result   array         if  is array  array             foreach   array as  k   gt   v                if  is array  v                      result   array merge  result  flatten  v                  else                    result      v                                     return  result

User · Answer

In PHP 5 6 and above you can flatten two dimensional arrays with array merge after unpacking the outer array with     operator  The code is simple and clear  array merge     a    This works with collection of associative arrays too   a     10  20    30  40     b      quot x quot    gt   quot X quot    quot y quot    gt   quot Y quot      quot p quot    gt   quot P quot    quot q quot    gt   quot Q quot      print r array merge     a    print r array merge     b     Array        0    gt  10      1    gt  20      2    gt  30      3    gt  40   Array        x    gt  X      y    gt  Y      p    gt  P      q    gt  Q    In PHP 8 0 and below  array unpacking does not work when the outer array has non numeric keys  Support for unpacking array with string keys is available from PHP 8 1  To support 8 0 and below  you should call array values first   c     quot a quot    gt    quot x quot    gt   quot X quot    quot y quot    gt   quot Y quot     quot b quot    gt    quot p quot    gt   quot P quot    quot q quot    gt   quot Q quot     print r array merge    array values  c      Array        x    gt  X      y    gt  Y      p    gt  P      q    gt  Q    Update  Based on comment by  MohamedGharib This will throw an error if the outer array is empty  since array merge would be called with zero arguments  It can be be avoided by adding an empty array as the first argument  array merge         a

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Because the code in here looks scary  Here is a function that will also convert a multidimensional array into html form compatible syntax  but which is easier to read          Flattens a multi demensional array into a one dimensional    to be compatible with hidden html fields         param array  array     Array in the form      array         a    gt  array           b    gt   1                       return array     Array in the form      array         a b     gt  1            function flatten array  array         Continue until  array is a one-dimensional array     continue   TRUE    while   continue         continue   FALSE          Walk through top and second level of  array and move         all values in the second level up one level      foreach   array as  key   gt   value          if  is array  value                Second level found  therefore continue           continue   TRUE              Move each value a level up          foreach   value as  child key   gt   child value               array  key          child key           child value                        Remove second level array from top level          unset  array  key                         return  array

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For those who just need to join one level below at the top  Being clearer  how transform this  Array                0    gt  Array                                0    gt  Array                                                id    gt  001                                        1    gt  Array                                                id    gt  005                                              1    gt  Array                                0    gt  Array                                                id    gt  007                                        1    gt  Array                                                id    gt  009                                            On this  Array                0    gt  Array                                0    gt  Array                                                id    gt  001                                        1    gt  Array                                                id    gt  005                                        2    gt  Array                                                id    gt  007                                        3    gt  Array                                                id    gt  009                                            The  simple  code  foreach   multi array as  key   gt   reduced array        foreach   reduced array as  key   gt   value             new array      value           With so many functions available  sometimes we forget that we can do something with a simple code

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Just thought I d point out that this is a fold  so array reduce can be used   array reduce  my array   array merge   array       EDIT  Note that this can be composed to flatten any number of levels  We can do this in several ways      Reduces one level  concat     function  x    return array reduce  x   array merge   array            We can compose  concat with itself  n times  then apply it to  x    This can overflow the stack for large  n  compose    function  f   g        return function  x  use   f   g    return  f  g  x           identity   function  x    return  x      flattenA   function  n  use   compose   identity   concat        return  function  x  use   compose   identity   concat   n            return   n     0    x                            call user func array reduce array fill 0   n   concat                                                           compose                                                          identity                                              x                 We can iteratively apply  concat to  x   n times  uncurriedFlip       function  f        return  function  a   b  use   f            return  f  b   a              iterate    function  f  use   uncurriedFlip        return  function  n  use   uncurriedFlip   f        return  function  x  use   uncurriedFlip   f   n            return   n     0    x                            array reduce array fill 0   n   f                                            uncurriedFlip  call user func                                             x                 flattenB    iterate  concat       Example usage   apply      function  f   x        return  f  x       curriedFlip   function  f        return  function  a  use   f        return  function  b  use   f   a            return  f  b   a                 var dump      array map          call user func  curriedFlip  apply                          array array array  A    B    C                                       array  D                                  array array                                       array  E               array  flattenA 2    flattenB 2        Of course  we could also use loops but the question asks for a combinator function along the lines of array map or array values

[php] How to Flatten a Multidimensional Array?

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