In PHP how do you change the key of an array element

Question

I have an associative array in the form key   gt  value where key is a numerical value  however it is not a sequential numerical value  The key is actually an ID number and the value is a count  This is fine for most instances  however I want a function that gets the human-readable name of the array and uses that for the key  without changing the value   I didn t see a function that does this  but I m assuming I need to provide the old key and new key  both of which I have  and transform the array  Is there an efficient way of doing this

User · Answer

if your array is built from a database query  you can change the key directly from the mysql statement   instead of   select   id   from   tablename         use something like    select   id     as NEWNAME   from   tablename

User · Answer

You can write simple function that applies the callback to the keys of the given array  Similar to array map   lt  php function array map keys callable  callback  array  array        return array merge        array map          function   key   value  use   callback    return   callback  key    gt   value              array keys  array            array             array     a    gt  1   b    gt   test    c    gt    x    gt  1   y    gt  2     newArray   array map keys function  key    return  new    ucfirst  key       array    echo json encode  array        a  1  b   test   c    x  1  y  2   echo json encode  newArray        newA  1  newB   test   newC    x  1  y  2     Here is a gist https   gist github com vardius 650367e15abfb58bcd72ca47eff096ca file-array map keys-php

User · Answer

This basic function handles swapping array keys and keeping the array in the original order     public function keySwap array  resource  array  keys         newResource            foreach  resource as  k   gt   r           if array key exists  k  keys                 newResource  keys  k      r           else               newResource  k     r                       return  newResource      You could then loop through and swap all  a  keys with  z  for example      inputs       0   gt    a   gt  1   b   gt  2      1   gt    a   gt  3   b   gt  4       keySwap     a   gt  z     foreach  inputs as  k  gt  i        inputs  k     this- gt keySwap  i  keySwap

User · Answer

This function will rename an array key  keeping its position  by combining with index searching   function renameArrKey  arr   oldKey   newKey       if  isset  arr  oldKey    return  arr     Failsafe      keys   array keys  arr        keys array search  oldKey   keys      newKey       newArr   array combine  keys   arr       return  newArr      Usage    arr   renameArrKey  arr   old key    new key

User · Answer

You can use this function based on array walk   function mapToIDs  array   id field name    id          result           array walk  array           function  amp  value   key  use   amp  result   id field name                         result  value  id field name      value                       return  result      arr    0   gt    id    gt   one    fruit    gt   apple    1   gt    id    gt   two    fruit    gt   banana     print r  arr   print r mapToIDs  arr      It gives   Array       0    gt  Array           id    gt  one          fruit    gt  apple            1    gt  Array           id    gt  two          fruit    gt  banana          Array       one    gt  Array           id    gt  one          fruit    gt  apple            two    gt  Array           id    gt  two          fruit    gt  banana

User · Answer

this code will help to change the oldkey to new one   i   0   keys array array  0   gt  one   1   gt  two      keys   array keys  keys array    for  i 0  i lt count  keys   i           keys array  keys array  i    keys array  i       unset  keys array  i      print r  keys array     display like   keys array array  one   gt  one   two   gt  two

User · Answer

best way is using reference  and not using unset  which make another step to clean memory    tab     two    gt          solution     tab  newname      amp   tab  two      you have one original and one reference with new name   or if you don t want have two names in one value is good make another tab and foreach on reference  foreach  tab as  key  gt   amp   value        if  key   two               newtab  newname      amp   tab  key          else            newtab  key     amp   tab  key              Iterration is better on keys than clone all array  and cleaning old array if you have long data like 100 rows     etc

User · Answer

If you want to replace several keys at once  preserving order           Rename keys of an array     param array  array  asoc      param array  replacement keys  indexed      return array     function rename keys  array   replacement keys           return array combine  replacement keys  array values  array        Usage    myarr   array  a    gt  22   b    gt  144   c    gt  43    newkeys   array  x   y   z    print r rename keys  myarr   newkeys      must return  array  x    gt  22   y    gt  144   z    gt  43

User · Answer

I like KernelM s solution  but I needed something that would handle potential key conflicts  where a new key may match an existing key   Here is what I came up with   function swapKeys   amp  arr   origKey   newKey   amp  pendingKeys         if   isset   arr  newKey                 arr  newKey     arr  origKey           unset   arr  origKey             if  isset   pendingKeys  origKey                       recursion to handle conflicting keys with conflicting keys             swapKeys   arr   pendingKeys  origKey    origKey   pendingKeys                unset   pendingKeys  origKey                     elseif   newKey     origKey              pendingKeys  newKey     origKey            You can then cycle through an array like this    myArray   array   1970-01-01 00 00 01    1970-01-01 00 01 00      pendingKeys   array    foreach   myArray as  key   gt   myArrayValue            NOTE  strtotime   1970-01-01 00 00 01      1  a conflicting key       timestamp   strtotime   myArrayValue        swapKeys   myArray   key   timestamp   pendingKeys         RESULT   myArray    array  1  gt  1970-01-01 00 00 01   60  gt  1970-01-01 00 01 00

User · Answer

Hmm  I m not test before  but I think this code working  function replace array key  data         mapping              old key 1    gt   new key 1            old key 2    gt   new key 2                data   json encode  data       foreach   mapping as  needed   gt   replace             data   str replace      needed            replace        data              return json decode  data  true

User · Answer

I like KernelM s solution  but I needed something that would handle potential key conflicts  where a new key may match an existing key   Here is what I came up with   function swapKeys   amp  arr   origKey   newKey   amp  pendingKeys         if   isset   arr  newKey                 arr  newKey     arr  origKey           unset   arr  origKey             if  isset   pendingKeys  origKey                       recursion to handle conflicting keys with conflicting keys             swapKeys   arr   pendingKeys  origKey    origKey   pendingKeys                unset   pendingKeys  origKey                     elseif   newKey     origKey              pendingKeys  newKey     origKey            You can then cycle through an array like this    myArray   array   1970-01-01 00 00 01    1970-01-01 00 01 00      pendingKeys   array    foreach   myArray as  key   gt   myArrayValue            NOTE  strtotime   1970-01-01 00 00 01      1  a conflicting key       timestamp   strtotime   myArrayValue        swapKeys   myArray   key   timestamp   pendingKeys         RESULT   myArray    array  1  gt  1970-01-01 00 00 01   60  gt  1970-01-01 00 01 00

User · Answer

You can use this function based on array walk   function mapToIDs  array   id field name    id          result           array walk  array           function  amp  value   key  use   amp  result   id field name                         result  value  id field name      value                       return  result      arr    0   gt    id    gt   one    fruit    gt   apple    1   gt    id    gt   two    fruit    gt   banana     print r  arr   print r mapToIDs  arr      It gives   Array       0    gt  Array           id    gt  one          fruit    gt  apple            1    gt  Array           id    gt  two          fruit    gt  banana          Array       one    gt  Array           id    gt  one          fruit    gt  apple            two    gt  Array           id    gt  two          fruit    gt  banana

User · Answer

You could use a second associative array that maps human readable names to the id s   That would also provide a Many to 1 relationship   Then do something like this    echo  Widgets       data  humanreadbleMapping  Widgets

User · Answer

The answer from KernelM is nice  but in order to avoid the issue raised by Greg in the comment  conflicting keys   using a new array would be safer   newarr  newkey     oldarr  oldkey    oldarr  newarr  unset  newarr

User · Answer

arr  newkey     arr  oldkey   unset  arr  oldkey

User · Answer

There is an alternative way to change the key of an array element when working with a full array - without changing the order of the array  It s simply to copy the array into a new array   For instance  I was working with a mixed  multi-dimensional array that contained indexed and associative keys - and I wanted to replace the integer keys with their values  without breaking the order   I did so by switching key value for all numeric array entries - here    0    foo    Note that the order is intact    lt  php  arr          foo        bar   gt  alfa        baz   gt   a   gt  hello    b   gt  world        foreach  arr as  k  gt  v         kk   is numeric  k     v    k       vv   is numeric  k    null    v       arr2  kk     vv     print r  arr2     Output   Array        foo    gt        bar    gt  alfa      baz    gt  Array                a    gt  hello              b    gt  world

User · Answer

Simple benchmark comparison of both solution  Solution 1 Copy and remove  order lost  but way faster  https   stackoverflow com a 240676 1617857  lt  php  array     test    gt   value      array  test2      array  test    unset  array  test      Solution 2 Rename the key https   stackoverflow com a 21299719 1617857  lt  php  array     test    gt   value      keys   array keys   array     keys array search  test    keys  true      test2   array combine   keys   array     Benchmark   lt  php  array     test    gt   value      for   i  0   i  lt  100000000   i            Solution 1     for   i  0   i  lt  100000000   i            Solution 2    Results  php solution1 php  6 33s  user 0 02s system 99  cpu 6 356  total php solution1 php  6 37s  user 0 01s system 99  cpu 6 390  total php solution2 php  12 14s user 0 01s system 99  cpu 12 164 total php solution2 php  12 57s user 0 03s system 99  cpu 12 612 total

User · Answer

This function will rename an array key  keeping its position  by combining with index searching   function renameArrKey  arr   oldKey   newKey       if  isset  arr  oldKey    return  arr     Failsafe      keys   array keys  arr        keys array search  oldKey   keys      newKey       newArr   array combine  keys   arr       return  newArr      Usage    arr   renameArrKey  arr   old key    new key

User · Answer

If you want to replace several keys at once  preserving order           Rename keys of an array     param array  array  asoc      param array  replacement keys  indexed      return array     function rename keys  array   replacement keys           return array combine  replacement keys  array values  array        Usage    myarr   array  a    gt  22   b    gt  144   c    gt  43    newkeys   array  x   y   z    print r rename keys  myarr   newkeys      must return  array  x    gt  22   y    gt  144   z    gt  43

User · Answer

There is an alternative way to change the key of an array element when working with a full array - without changing the order of the array  It s simply to copy the array into a new array   For instance  I was working with a mixed  multi-dimensional array that contained indexed and associative keys - and I wanted to replace the integer keys with their values  without breaking the order   I did so by switching key value for all numeric array entries - here    0    foo    Note that the order is intact    lt  php  arr          foo        bar   gt  alfa        baz   gt   a   gt  hello    b   gt  world        foreach  arr as  k  gt  v         kk   is numeric  k     v    k       vv   is numeric  k    null    v       arr2  kk     vv     print r  arr2     Output   Array        foo    gt        bar    gt  alfa      baz    gt  Array                a    gt  hello              b    gt  world

User · Answer

array          old1    gt  1      old2    gt  2      renameMap          old1    gt   new1           old2    gt   new2       array   array combine array map function  el  use   renameMap        return  renameMap  el      array keys  array    array values  array         array          new1    gt  1      new2    gt  2

User · Answer

The way you would do this and preserve the ordering of the array is by putting the array keys into a separate array  find and replace the key in that array and then combine it back with the values    Here is a function that does just that   function change key   array   old key   new key          if    array key exists   old key   array             return  array        keys   array keys   array         keys  array search   old key   keys        new key       return array combine   keys   array

User · Answer

best way is using reference  and not using unset  which make another step to clean memory    tab     two    gt          solution     tab  newname      amp   tab  two      you have one original and one reference with new name   or if you don t want have two names in one value is good make another tab and foreach on reference  foreach  tab as  key  gt   amp   value        if  key   two               newtab  newname      amp   tab  key          else            newtab  key     amp   tab  key              Iterration is better on keys than clone all array  and cleaning old array if you have long data like 100 rows     etc

User · Answer

Hmm  I m not test before  but I think this code working  function replace array key  data         mapping              old key 1    gt   new key 1            old key 2    gt   new key 2                data   json encode  data       foreach   mapping as  needed   gt   replace             data   str replace      needed            replace        data              return json decode  data  true

User · Answer

If your array is recursive you can use this function  test this data        datos   array                0    gt  array                                no    gt  1                   id maquina    gt  1                   id transaccion    gt  1276316093                   ultimo cambio    gt   asdfsaf                    fecha ultimo mantenimiento    gt  1275804000                   mecanico ultimo mantenimiento    gt  asdfas                    fecha ultima reparacion    gt  1275804000                   mecanico ultima reparacion    gt   sadfasf                    fecha siguiente mantenimiento    gt  1275804000                   fecha ultima falla    gt  0                   total fallas    gt  0                           1    gt  array                                no    gt  2                   id maquina    gt  2                   id transaccion    gt  1276494575                   ultimo cambio    gt   xx                    fecha ultimo mantenimiento    gt  1275372000                   mecanico ultimo mantenimiento    gt   xx                    fecha ultima reparacion    gt  1275458400                   mecanico ultima reparacion    gt   xx                    fecha siguiente mantenimiento    gt  1275372000                   fecha ultima falla    gt  0                   total fallas    gt  0                         here is the function   function changekeyname  array   newkey   oldkey       foreach   array as  key   gt   value              if  is array  value             array  key    changekeyname  value  newkey  oldkey         else                         array  newkey      array  oldkey                          unset  array  oldkey                 return  array

User · Answer

arr  newkey     arr  oldkey   unset  arr  oldkey

User · Answer

array          old1    gt  1      old2    gt  2      renameMap          old1    gt   new1           old2    gt   new2       array   array combine array map function  el  use   renameMap        return  renameMap  el      array keys  array    array values  array         array          new1    gt  1      new2    gt  2

User · Answer

You could use a second associative array that maps human readable names to the id s   That would also provide a Many to 1 relationship   Then do something like this    echo  Widgets       data  humanreadbleMapping  Widgets

User · Answer

Easy stuff   this function will accept the target  hash and  replacements is also a hash containing newkey  oldkey associations   This function will preserve original order  but could be problematic for very large  like above 10k records  arrays regarding performance  amp  memory   function keyRename array  hash  array  replacements         new array        foreach  hash as  k  gt  v                if  ok array search  k  replacements                k  ok           new  k   v            return  new          this alternative function would do the same  with far better performance  amp  memory usage  at the cost of loosing original order  which should not be a problem since it is hashtable    function keyRename array  hash  array  replacements         foreach  hash as  k  gt  v          if  ok array search  k  replacements                        hash  ok   v            unset  hash  k                   return  hash

User · Answer

if your array is built from a database query  you can change the key directly from the mysql statement   instead of   select   id   from   tablename         use something like    select   id     as NEWNAME   from   tablename

User · Answer

this code will help to change the oldkey to new one   i   0   keys array array  0   gt  one   1   gt  two      keys   array keys  keys array    for  i 0  i lt count  keys   i           keys array  keys array  i    keys array  i       unset  keys array  i      print r  keys array     display like   keys array array  one   gt  one   two   gt  two

User · Answer

If your array is recursive you can use this function  test this data        datos   array                0    gt  array                                no    gt  1                   id maquina    gt  1                   id transaccion    gt  1276316093                   ultimo cambio    gt   asdfsaf                    fecha ultimo mantenimiento    gt  1275804000                   mecanico ultimo mantenimiento    gt  asdfas                    fecha ultima reparacion    gt  1275804000                   mecanico ultima reparacion    gt   sadfasf                    fecha siguiente mantenimiento    gt  1275804000                   fecha ultima falla    gt  0                   total fallas    gt  0                           1    gt  array                                no    gt  2                   id maquina    gt  2                   id transaccion    gt  1276494575                   ultimo cambio    gt   xx                    fecha ultimo mantenimiento    gt  1275372000                   mecanico ultimo mantenimiento    gt   xx                    fecha ultima reparacion    gt  1275458400                   mecanico ultima reparacion    gt   xx                    fecha siguiente mantenimiento    gt  1275372000                   fecha ultima falla    gt  0                   total fallas    gt  0                         here is the function   function changekeyname  array   newkey   oldkey       foreach   array as  key   gt   value              if  is array  value             array  key    changekeyname  value  newkey  oldkey         else                         array  newkey      array  oldkey                          unset  array  oldkey                 return  array

User · Answer

Easy stuff   this function will accept the target  hash and  replacements is also a hash containing newkey  oldkey associations   This function will preserve original order  but could be problematic for very large  like above 10k records  arrays regarding performance  amp  memory   function keyRename array  hash  array  replacements         new array        foreach  hash as  k  gt  v                if  ok array search  k  replacements                k  ok           new  k   v            return  new          this alternative function would do the same  with far better performance  amp  memory usage  at the cost of loosing original order  which should not be a problem since it is hashtable    function keyRename array  hash  array  replacements         foreach  hash as  k  gt  v          if  ok array search  k  replacements                        hash  ok   v            unset  hash  k                   return  hash

User · Answer

The way you would do this and preserve the ordering of the array is by putting the array keys into a separate array  find and replace the key in that array and then combine it back with the values    Here is a function that does just that   function change key   array   old key   new key          if    array key exists   old key   array             return  array        keys   array keys   array         keys  array search   old key   keys        new key       return array combine   keys   array

User · Answer

If you want also the position of the new array key to be the same as the old one you can do this   function change array key   array   old key   new key        if  is array  array    print  You must enter a array as a haystack    exit        if  array key exists  old key   array            return  array              key pos   array search  old key  array keys  array         arr before   array slice  array  0   key pos        arr after   array slice  array   key pos   1        arr renamed   array  new key   gt   array  old key         return  arr before    arr renamed    arr after

User · Answer

Here is a helper function to achieve that          Helper function to rename array keys      function  rename arr key  oldkey   newkey  array  amp  arr        if  array key exists  oldkey   arr              arr  newkey     arr  oldkey           unset  arr  oldkey            return TRUE        else           return FALSE            pretty based on  KernelM answer   Usage    rename arr key  oldkey    newkey    my array     It will return true on successful rename  otherwise false

User · Answer

this works for renaming the first key    a     catine    gt   cat    canine     gt   dog     tmpa  feline      a  catine    unset  a  catine      a    tmpa    a    then  print r  a  renders a repaired in-order array   Array        feline    gt  cat      canine    gt  dog     this works for renaming an arbitrary key    a     canine     gt   dog    catine    gt   cat    porcine    gt   pig    af   array flip  a   af  cat      feline    a   array flip  af    print r  a   Array        canine    gt  dog      feline    gt  cat      porcine    gt  pig     a generalized function   function renameKey  oldkey   newkey   array         val    array  oldkey        tmp A   array flip  array        tmp A  val     newkey       return array flip  tmp A

User · Answer

One which preservers ordering that s simple to understand   function rename array key array  array   old key   new key      if   array key exists  old key   array           return  array         new array         foreach   array as  key   gt   value         new key    old key      key          new key          key       new array  new key     value        return  new array

User · Answer

arr  newkey     arr  oldkey   unset  arr  oldkey

User · Answer

This basic function handles swapping array keys and keeping the array in the original order     public function keySwap array  resource  array  keys         newResource            foreach  resource as  k   gt   r           if array key exists  k  keys                 newResource  keys  k      r           else               newResource  k     r                       return  newResource      You could then loop through and swap all  a  keys with  z  for example      inputs       0   gt    a   gt  1   b   gt  2      1   gt    a   gt  3   b   gt  4       keySwap     a   gt  z     foreach  inputs as  k  gt  i        inputs  k     this- gt keySwap  i  keySwap

User · Answer

One which preservers ordering that s simple to understand   function rename array key array  array   old key   new key      if   array key exists  old key   array           return  array         new array         foreach   array as  key   gt   value         new key    old key      key          new key          key       new array  new key     value        return  new array

User · Answer

You could use a second associative array that maps human readable names to the id s   That would also provide a Many to 1 relationship   Then do something like this    echo  Widgets       data  humanreadbleMapping  Widgets

User · Answer

Here is a helper function to achieve that          Helper function to rename array keys      function  rename arr key  oldkey   newkey  array  amp  arr        if  array key exists  oldkey   arr              arr  newkey     arr  oldkey           unset  arr  oldkey            return TRUE        else           return FALSE            pretty based on  KernelM answer   Usage    rename arr key  oldkey    newkey    my array     It will return true on successful rename  otherwise false

User · Answer

You could use a second associative array that maps human readable names to the id s   That would also provide a Many to 1 relationship   Then do something like this    echo  Widgets       data  humanreadbleMapping  Widgets

User · Answer

The answer from KernelM is nice  but in order to avoid the issue raised by Greg in the comment  conflicting keys   using a new array would be safer   newarr  newkey     oldarr  oldkey    oldarr  newarr  unset  newarr

User · Answer

If you want also the position of the new array key to be the same as the old one you can do this   function change array key   array   old key   new key        if  is array  array    print  You must enter a array as a haystack    exit        if  array key exists  old key   array            return  array              key pos   array search  old key  array keys  array         arr before   array slice  array  0   key pos        arr after   array slice  array   key pos   1        arr renamed   array  new key   gt   array  old key         return  arr before    arr renamed    arr after

User · Answer

this works for renaming the first key    a     catine    gt   cat    canine     gt   dog     tmpa  feline      a  catine    unset  a  catine      a    tmpa    a    then  print r  a  renders a repaired in-order array   Array        feline    gt  cat      canine    gt  dog     this works for renaming an arbitrary key    a     canine     gt   dog    catine    gt   cat    porcine    gt   pig    af   array flip  a   af  cat      feline    a   array flip  af    print r  a   Array        canine    gt  dog      feline    gt  cat      porcine    gt  pig     a generalized function   function renameKey  oldkey   newkey   array         val    array  oldkey        tmp A   array flip  array        tmp A  val     newkey       return array flip  tmp A

User · Answer

You can write simple function that applies the callback to the keys of the given array  Similar to array map   lt  php function array map keys callable  callback  array  array        return array merge        array map          function   key   value  use   callback    return   callback  key    gt   value              array keys  array            array             array     a    gt  1   b    gt   test    c    gt    x    gt  1   y    gt  2     newArray   array map keys function  key    return  new    ucfirst  key       array    echo json encode  array        a  1  b   test   c    x  1  y  2   echo json encode  newArray        newA  1  newB   test   newC    x  1  y  2     Here is a gist https   gist github com vardius 650367e15abfb58bcd72ca47eff096ca file-array map keys-php

User · Answer

arr  newkey     arr  oldkey   unset  arr  oldkey

User · Answer

Simple benchmark comparison of both solution  Solution 1 Copy and remove  order lost  but way faster  https   stackoverflow com a 240676 1617857  lt  php  array     test    gt   value      array  test2      array  test    unset  array  test      Solution 2 Rename the key https   stackoverflow com a 21299719 1617857  lt  php  array     test    gt   value      keys   array keys   array     keys array search  test    keys  true      test2   array combine   keys   array     Benchmark   lt  php  array     test    gt   value      for   i  0   i  lt  100000000   i            Solution 1     for   i  0   i  lt  100000000   i            Solution 2    Results  php solution1 php  6 33s  user 0 02s system 99  cpu 6 356  total php solution1 php  6 37s  user 0 01s system 99  cpu 6 390  total php solution2 php  12 14s user 0 01s system 99  cpu 12 164 total php solution2 php  12 57s user 0 03s system 99  cpu 12 612 total

[php] In PHP, how do you change the key of an array element?

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