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Last updated: Thu, 19 May 2005

array_merge

(PHP 4, PHP 5)

array_merge -- Merge one or more arrays

Description

array array_merge ( array array1 [, array array2 [, array ...]] )

array_merge() merges the elements of one or more arrays together so that the values of one are appended to the end of the previous one. It returns the resulting array.

If the input arrays have the same string keys, then the later value for that key will overwrite the previous one. If, however, the arrays contain numeric keys, the later value will not overwrite the original value, but will be appended.

If only one array is given and the array is numerically indexed, the keys get reindexed in a continuous way.

Example 1. array_merge() example

<?php
$array1 = array("color" => "red", 2, 4);
$array2 = array("a", "b", "color" => "green", "shape" => "trapezoid", 4);
$result = array_merge($array1, $array2);
print_r($result);
?>

The above example will output:

Array
(
   [color] => green
   [0] => 2
   [1] => 4
   [2] => a
   [3] => b
   [shape] => trapezoid
   [4] => 4
)

Example 2. Simple array_merge() example

<?php
$array1 = array();
$array2 = array(1 => "data");
$result = array_merge($array1, $array2);
?>

Don't forget that numeric keys will be renumbered!

Array
(
   [0] => data
)

If you want to completely preserve the arrays and just want to append them to each other, use the + operator:

<?php
$array1 = array();
$array2 = array(1 => "data");
$result = $array1 + $array2;
?>

The numeric key will be preserved and thus the association remains.

Array
(
   [1] => data
)

Warning

The behavior of array_merge() was modified in PHP 5. Unlike PHP 4, array_merge() now only accepts parameters of type array. However, you can use typecasting to merge other types. See the example below for details.

Example 3. array_merge() PHP 5 example

<?php
$beginning = 'foo';
$end = array(1 => 'bar');
$result = array_merge((array)$beginning, (array)$end);
print_r($result);
?>

The above example will output:

Array
(
   [0] => foo
   [1] => bar
)

See also array_merge_recursive(), array_combine() and array operators.



User Contributed Notes
array_merge
rafmavCHEZlibre_in_france
19-Apr-2005 06:54
Here are a few functions to make a diff between two arrays (or 2 strings, see the example) and merge it back after
<?
function array_diff_both($new,$old)
{
   $del=array_diff_assoc($old,$new);
   $add=array_diff_assoc($new,$old);
   return $diff=array("del"=>$del, "add"=>$add);
}

function array_diff_all($arr_new,$arr_old)
{
   $arr_equ=array_intersect_assoc($arr_new,$arr_old);
   $arr_del=array_diff_assoc($arr_old,$arr_new);
   $arr_add=array_diff_assoc($arr_new,$arr_old);
   return $diff=array("equ"=>$arr_equ, "del"=>$arr_del, "add"=>$arr_add);
}

function array_merge_diff($arr,$diff) {
   $arr=array_merge_replace($arr,$diff["del"]);
   $arr=array_merge_replace($arr,$diff["add"]);
   return $arr;
}
function array_merge_diff_reverse($arr,$diff) {
   $arr=array_merge_replace($arr,$diff["add"]);
   $arr=array_merge_replace($arr,$diff["del"]);
   return $arr;
}
?>
Here is an example:
<?
//calculationg
$new="hello!"; // new string

$old="hrllo!"; // old string with a typo fault

// cast string in array the goodway
// make a cast (array) to a string does not work:
// the entire string is thus considered as one element
// of the array !!
$a_new=str_split($new);
$a_old=str_split($old); // cast string in array

$diff=array_diff_both($a_new,$a_old); // the entire diff

$test=array_merge_diff($a_old,$diff);

$test_reverse=array_merge_diff_reverse($a_new,$diff);

//for output the sample
print "new= $new<br/>old= $old<br/>\$a_new= ";
print_r($a_new);

print "<br/>\$a_old= ";
print_r($a_old);

print "<br/>\$diff=\$a_new-\$a_old";
print "<br/>\$diff= ";
print_r($diff);

print "<br/>\$test=\$a_old+\$diff";
print "<br/>\$test= ";
print_r($test);
print("<br/>".implode($test));

print "<br/>\$test_reverse=\$a_new+\$diff";
print "<br/>\$test_reverse= ";
print_r($test_reverse);
print("<br/>".implode($test_reverse));
?>
En sortie de l'exemple, résultats:

new= hello!
old= hrllo!
$a_new= Array ( [0] => h [1] => e [2] => l [3] => l [4] => o [5] => ! )
$a_old= Array ( [0] => h [1] => r [2] => l [3] => l [4] => o [5] => ! )
$diff=$a_new-$a_old
$diff= Array ( [del] => Array ( [1] => r ) [add] => Array ( [1] => e ) )
$test=$a_old+$diff
$test= Array ( [0] => h [1] => e [2] => l [3] => l [4] => o [5] => ! )
hello!
$test_reverse=$a_new+$diff
$test_reverse= Array ( [0] => h [1] => r [2] => l [3] => l [4] => o [5] => ! )
hrllo!

autre exemple, autre résultat:
new= see you!
old= sea ya!
$a_new= Array ( [0] => s [1] => e [2] => e [3] => [4] => y [5] => o [6] => u [7] => ! )
$a_old= Array ( [0] => s [1] => e [2] => a [3] => [4] => y [5] => a [6] => ! )
$diff=$a_new-$a_old
$diff= Array ( [del] => Array ( [2] => a [5] => a [6] => ! ) [add] => Array ( [2] => e [5] => o [6] => u [7] => ! ) )
$test=$a_old+$diff
$test= Array ( [0] => s [1] => e [2] => e [3] => [4] => y [5] => o [6] => u [7] => ! )
see you!
$test_reverse=$a_new+$diff
$test_reverse= Array ( [0] => s [1] => e [2] => a [3] => [4] => y [5] => a [6] => ! [7] => ! )
sea ya!!
Vinicius Cubas Brand
14-Apr-2005 11:32
The following function merges two arrays taking as parameter an user-defined comparison function:

<?
   function array_merge_custom(&$array1,&$array2,$comparison_func)
   {
       $ret_arr = array();
       foreach ($array1 as $key1 => $element1)
       {
           $has_equal_in_2 = false;
           foreach($array2 as $key2 => $element2)
           {
               if (call_user_func($comparison_func,$element1,$element2))
               {
                   $has_equal_in_2 = true;
               }
           }
           if (!$has_equal_in_2)
           {
               $ret_arr[] = $array1[$key1];
           }
       }
       $ret_arr = array_merge($ret_arr,$array2);
       return $ret_arr;
   }

?>

For instance:

<?

   $a = array(
       array('index' => 'ball', 'blabla' => 0),
       array('index' => 'coconut'),
       array('index' => 'cow'),
       array('index' => 'son'),
       );

   $b = array(
       array('index' => 'phone'),
       array('index' => 'wallet'),
       array('index' => 'ball'),
       array('index' => 'son', 'kabum'=> 1)
       );

   $c = array_merge_custom($a,$b,create_function('$a,$b','return $a[\'index\'] == $b[\'index\'];'));
   print_r($c)
?>

Will produce:

Array
(
   [0] => Array
       (
           [index] => coconut
       )
   [1] => Array
       (
           [index] => cow
       )
   [2] => Array
       (
           [index] => phone
       )
   [3] => Array
       (
           [index] => wallet
       )
   [4] => Array
       (
           [index] => ball
       )
   [5] => Array
       (
           [index] => son
           [kabum] => 1
       )
)
jeff_1089 at yahoo dot com
06-Apr-2005 03:17
Note that casting the array doesn't always work.  For classes, it looks like the class information is lost.  The print_r's below have different behavior.  I would suggest creating an array, rather than casting in most situations. (ie.  do it like $array2).

class myclass {
   private $name;
   private $value;
   function myclass($n, $v) {
       $this->name=$n;
       $this->value=$v;
   }   
}

$itema = new myclass("hair", "orange");
$itemb = new myclass("eyes", "green");
$itemc = new myclass("elbow", "dirty");
$items = array($itemb, $itemc);
print "<BR>";
$array1 = array_merge((array)$itema, $items);
$array2 = array_merge(array($itema), $items);
print "<BR>";
print "<BR>";
print_r($array1);
print "<BR>";
print "<BR>";
print_r($array2);

Array ( [] => orange [0] => myclass Object ( [name:private] => eyes [value:private] => green ) [1] => myclass Object ( [name:private] => elbow [value:private] => dirty ) )

Array ( [0] => myclass Object ( [name:private] => hair [value:private] => orange ) [1] => myclass Object ( [name:private] => eyes [value:private] => green ) [2] => myclass Object ( [name:private] => elbow [value:private] => dirty ) )
lito at eordes dot com
20-Mar-2005 05:54
This is a simple function to merge an array multidimensional:

<?php
  function multimerge ($array1, $array2) {
   if (is_array($array2) && count($array2)) {
     foreach ($array2 as $k => $v) {
       if (is_array($v) && count($v)) {
         $array1[$k] = multimerge($array1[$k], $v);
       } else {
         $array1[$k] = $v;
       }
     }
   } else {
     $array1 = $array2;
   }

   return $array1;
  }

$array1 = array(
  1 => "value1",
  2 => "value2",
  3 => array(
   "valor2" => "test3",
  ),
  "more" => array(
   "alot" => "A lot of values",
   ":)" => "Cont"
  )
);

$array2 = array(
  2 => "other value",
  3 => array(
   "valor3" => "more values",
  ),
  "more" => array(
   "alot" => "Change the value"
  ),
  "final" => "Final Value"
);

print_r(multimerge($array1, $array2));
?>

The output is:

Array
(
   [1] => value1
   [2] => other value
   [3] => Array
       (
           [valor2] => test3
           [valor3] => more values
       )

   [more] => Array
       (
           [alot] => Change the value
           [:)] => Cont
       )

   [final] => Final Value
)
Jimomighty
20-Mar-2005 12:48
...

function preserved_merge_array( $newArray, $otherArray ) {
   foreach( $otherArray as $key => $value)
   {
       if ( !is_array($newArray[$key]) ) $newArray[$key] = array();
       if ( is_array($value) ) $newArray[$key] = preserved_merge_array( $newArray[$key], $value );
       else $newArray[$key] = $value;
   }
  
   return $newArray;
}

...
Alec Solway
20-Jan-2005 12:05
Note that if you put a number as a key in an array, it is eventually converted to an int even if you cast it to a string or put it in quotes.

That is:

$arr["0"] = "Test";
var_dump( key($arr) );

will output int(0).

This is important to note when merging because array_merge will append values with a clashing int-based index instead of replacing them. This kept me tied up for hours.
nospam at veganismus dot ch
11-Jan-2005 08:38
Someone posted a function with the note:
"if u need to overlay a array that holds defaultvalues with another that keeps the relevant data"

<?
//about twice as fast but the result is the same.
//note: the sorting will be messed up!
function array_overlay($skel, $arr) {
   return $arr+$skel;
}

//example:
$a = array("zero","one","two");
$a = array_overlay($a,array(1=>"alpha",2=>NULL));
var_dump($a);
/* NULL is ignored so the output is:
array(3) {
  [1]=>
  string(5) "alpha"
  [0]=>
  string(4) "zero"
  [2]=>
  string(3) "two"
}
*/
?>
Frederick.Lemasson{AT}kik-it.com
23-Dec-2004 04:57
if you generate form select from an array, you probably want to keep your array keys and order intact,
if so you can use ArrayMergeKeepKeys(), works just like array_merge :

array ArrayMergeKeepKeys ( array array1 [, array array2 [, array ...]])

but keeps the keys even if of numeric kind.
enjoy

<?

$Default[0]='Select Something please';

$Data[147]='potato';
$Data[258]='banana';
$Data[54]='tomato';

$A=array_merge($Default,$Data);

$B=ArrayMergeKeepKeys($Default,$Data);

echo '<pre>';
print_r($A);
print_r($B);
echo '</pre>';

Function ArrayMergeKeepKeys() {
     $arg_list = func_get_args();
     foreach((array)$arg_list as $arg){
         foreach((array)$arg as $K => $V){
             $Zoo[$K]=$V;
         }
     }
   return $Zoo;
}

//will output :

Array
(
   [0] => Select Something please
   [1] => potato
   [2] => banana
   [3] => tomato
)
Array
(
   [0] => Select Something please
   [147] => potato
   [258] => banana
   [54] => tomato
)

?>
jnothman at student dot usyd dot edu dot au
25-Nov-2004 12:40
If you have a two dimensional array, or otherwise an array of arrays, the following may be handy: <?call_user_func_array('array_merge', $arr);?>

For instance:
<?php
list($GIF, $JPG, $PNG, $WBMP) = array(1,2,3,15);
$ext_map = array(
   $GIF  => array('gif'),
   $JPG  => array('jpg', 'jpeg'),
   $PNG  => array('png'),
   $WBMP => array('wbmp'),
);
$ext_list = call_user_func_array('array_merge', $ext_map);
print_r($ext_list);
?>

Output:
Array
(
   [0] => gif
   [1] => jpg
   [2] => jpeg
   [3] => png
   [4] => wbmp
)
Jae
22-Nov-2004 09:17
This is explained above but may not be exactly clear.  If you have two arrays such as:

$Array1 {

[0] => "dog"

}

$Array2 {

[0] => "cat",
[1] => "bird",
[2] => null,
...
[n-1] => null,
[n] => "gator"
}

and you don't want to lose the null values in the final array then do NOT use array_merge.  Instead simply use the + operator.

array_merge($Array1,$Array2) gives:
[0] => "dog",
[1] => "cat",
[2] => "bird",
[3] => "gator"

$Array1 + $Array2 gives:
[0] => "dog",
[1] => "cat",
[2] => "bird",
[3] => null,
...
[n-1] => null,
[3] => "gator"
17-Nov-2004 12:22
function array_overlay($skel, $arr)
{
   foreach ($skel as $key => $val) {
       if (!isset($arr[$key])) {
           $arr[$key] = $val;
       } else {
           if (is_array($val)) {
               $arr[$key] = array_overlay($val, $arr[$key]);
           }
       }
   }

   return $arr;
}

// if u need to overlay a array that holds defaultvalues with another that keeps the relevant data
nospam at veganismus dot ch
25-Sep-2004 10:48
I needed to add some values (array) to an array on each loop.
I used merge because it seemed to be the right way. But array_splice() ist much faster:

<?
$merge = array();
$splice = array();

function makearray() { //to do on each loop
 //return two values:
 return array('foo','bar');
}

for($i=0;$i<1000;$i++) $merge = array_merge($merge,makearray());
echo count($merge); //returns 2000 after about 2 sec (PHP5)

for($i=0;$i<1000;$i++) array_splice($splice, 0,0,makearray());
echo count($splice); //returns 2000 after about 0.8 sec (PHP5)
?>

Note: The sorting will be diffrent but you can use
array_splice($splice, count($splice),0,makearray());
which is still faster (1.4 sec)
bcraigie at bigfoot dot com
24-Aug-2004 02:37
It would seem that array_merge doesn't do anything when one array is empty (unset):

<?php //$a is unset
$b = array("1" => "x");

$a = array_merge($a, $b});

//$a is still unset.
?>

to fix this omit $a if it is unset:-

<?php
if(!IsSet($a)) {
   $a = array_merge($b);
} else {
  $a = array_merge($a, $b);
}
?>

I don't know if there's a better way.
niv at NOSPAM iaglans dot DE
12-Jun-2004 12:18
[Editor's Note: If the keys are truly numeric, array_merge will do the trick. But if they are strings, as the example below, you can use array_merge(array_values($array1), array_values($array2)); since it's more beautiful. -- victor@php.net]

i recognized there is no function with that you can add two number-Arrays:

Example:

<?php
// you have two arrays:

array1 = array (['0'] =>"blahblupp",
                       ['1'] => "bluppblah" );

array2 = array (['0'] =>"tirili",
                       ['1'] => "tralala" );

// and want following as a result:

result = array (['0'] =>"blahblupp",
                     ['1'] => "bluppblah",
                     ['2'] =>"tirili",
                     ['3'] => "tralala" );

// following function does the addition:

function array_add($array1, $array2)
{
   $result = $array1;
   $h = sizeof($array1);
   for ($i = 0; $i < sizeof($array2); $i++)
   {
       $result[$h] = $array2[$i];
       $h++;
   }
  
   return $result;
}
?>

just added because I didn't find a ready-to-use script here.
mail at nospam dot iaindooley dot com
08-Apr-2004 11:37
hey there, here is a nice little way of merging two arrays that may or may not have numerical or string indices and preserving the order and indexing of both arrays whilst making the most use of in built php functions (i actually originally wanted to use array_combine for obvious reasons but seeing as that is not available in PHP4, the little foreach loop at the end is necessary):

<?php
       function merge($arr1,$arr2)
       {
               if(!is_array($arr1))
                       $arr1 = array();
               if(!is_array($arr2))
                       $arr2 = array();
               $keys1 = array_keys($arr1);
               $keys2 = array_keys($arr2);
               $keys  = array_merge($keys1,$keys2);
               $vals1 = array_values($arr1);
               $vals2 = array_values($arr2);
               $vals  = array_merge($vals1,$vals2);
               $ret    = array();

               foreach($keys as $key)
               {
                       list($unused,$val) = each($vals);
                       $ret[$key] = $val;
               }

           return $ret;
       }
?>
frankb at fbis dot net
25-Feb-2004 06:02
to merge arrays and preserve the key i found the following working with php 4.3.1:

<?php
$array1 = array(1 => "Test1", 2 => "Test2");
$array2 = array(3 => "Test3", 4 => "Test4");

$array1 += $array2;
?>

dont know if this is working with other php versions but it is a simple and fast way to solve that problem.
KOmaSHOOTER at gmx dot de
07-Nov-2003 12:03
Here is something for splitting a sorted array into group array  ( sorting the group arrays ) and then merging them together
Note: merge is  like concat in Flash ActionScript :)
In this example i have 3 different  groups in one array

* First the mainArray is sorted for the group entrys
* building from part arrays
* building  copy arrays from  part arrays ( for making the array beginning with  [0] !! )
* merging all part arrays together

0. sorting the main array
1. apportionment from the main array
when the group is changing , a new array is build (part
array ) ! attention at the second  part array !! Array values
are are not beginning with [0]!!
2. making the copy from the part array .
array values are pushed in the new array
3. echo for every array entry
4. overwriting the old array with the new copy
5. part arrays are sorted by function (arrays had been naughted by function array_copy ( Array is beginning with [0] ! )
6. merging the part arrays

Here is the same that i posted before but a bit better solved
array_push (${"activ_array".$j}, $activ_array[$i]); makes the part arrays starting with [0] :)

<?php
$activ_array=array(
array("apfel_01","germany","xx","red"),
array("apfel_07","germany","xx","green"),
array("apfel_08","germany","xx","green"),
array("apfel_02","germany","xx","red"),
array("apfel_03","germany","xx","red"),
array("apfel_04","germany","xx","red"),
array("apfel_09","germany","xx","red_+_green"),
array("apfel_10","germany","xx","red_+_green"),
array("apfel_05","germany","xx","green"),
array("apfel_06","germany","xx","green")
);
function array_sort($array, $key , $target){
for ($i = 0; $i < sizeof($array); $i++){
 $array2 = $array;
 if($target == 'name'){
   if(! empty($array2[$i]["nameletter"])){
     //echo $myarray[$i]["nameletter"] ;
     $array2[$i]["name"] = substr($array2[$i][$key],($array2[$i]["nameletter"]-1));
   }else{
     $array2[$i]["name"] = substr($array2[$i][$key],0);
   }
   $sort_values[$i] = $array2[$i]["name"];
   }else{
   $sort_values[$i] = $array2[$i][$key];
 }
}
  asort ($sort_values);
  reset ($sort_values);
  while (list ($arr_keys, $arr_values) = each ($sort_values)) {
         $sorted_arr[] = $array[$arr_keys];
  }
  return $sorted_arr;
}
$activ_array = array_sort($activ_array,3,'imagetype');
$j=0;
// first part array
${"activ_array"."$j"} = array();
for($i=0;$i<sizeof($activ_array);$i++){
 if($activ_array[$i][3] !=$activ_array[$i-1][3] && $i >1){
   $j++;
   ${"activ_array".$j} = array();
 }
array_push (${"activ_array".$j}, $activ_array[$i]);
}
// part array sorting
for($i=0;$i<=$j;$i++){
 ${"activ_array".$i} = array_sort(${"activ_array".$i},0,'name');
}
$activ_array = array();
for($i=0;$i<=$j;$i++){
 $activ_array = array_merge($activ_array,${"activ_array".$i});
}
for($i=0;$i<sizeof($activ_array);$i++){
print_r($activ_array[$i]);
echo("<br>");
}

?>
rcarvalhoREMOVECAPS at clix dot pt
03-Nov-2003 02:43
While searching for a function that would renumber the keys in a array, I found out that array_merge() does this if the second parameter is null:

Starting with array $a like:

<?php
Array
(
   [5] => 5
   [4] => 4
   [2] => 2
   [9] => 9
)
?>

Then use array_merge() like this:

<?php
$a = array_merge($a, null);
?>

Now the $a array has bee renumbered, but maintaining the order:

<?php
Array
(
   [0] => 5
   [1] => 4
   [2] => 2
   [3] => 9
)
?>

Hope this helps someone :-)
01-Nov-2003 12:08
In all PHP 4 versions the above function deals gracefully with paramaters which are NOT arrays(). So if you pass a string or number it will be automagically converted to an one-element array as described in the manual section about Types and "implicit typecasting". So if you ever happen to put an empty/unset variable (NULL value) as parameter, array_merge() will still collapse the other arrays as intended.

From PHP5beta2 on this behaviour changed, and PHP will correctly issue a E_WARNING message, whenever one of the paramters isn't an array. So if you ever happen to be uncertain about the contents of a variable passed as parameter to array_merge() you should use explicit typecasting:

<?php
$a = array(1, 2, 3);
$b = 4;    #-- beware: this is no array!

$result = array_merge(  (array)$a, (array)$b,  ... );
?>

This way $result still would get == array(1, 2, 3, 4); where otherwise the parameters would get rejected with the warning message telling you so.
loner at psknet dot !NOSPAM!com
29-Sep-2003 05:00
I got tripped up for a few days when I tried to merge a (previously serialized) array into a object. If it doesn't make sense, think about it... To someone fairly new, it could... Anyway, here is what I did:
(It's obviously not recursive, but easy to make that way)
<?php
function array_object_merge(&$object, $array) {
   foreach ($array as $key => $value)
       $object->{$key} = $value;
}
?>

Simple problem, but concevibly easy to get stuck on.
ice at lazybytes dot net
05-Sep-2003 05:31
I, too have found array_merge_clobber() useful. I use it in a loop to append data to an array. However, when the loop first runs, there will be an error message displayed as array one is empty, so, here is a little fix:

<?php
function array_merge_clobber($arrOne,$arrTwo) {
   if(!is_array($arrOne) || !is_array($arrTwo)) return false;

   $arrNewArray = $arrOne;
   forEach ($arrTwo as $key => $val) {
       if (isSet($arrNewArray[$key])) {
           if (is_array($val) && is_array($arrNewArray[$key])) {
               $arrNewArray[$key] = array_merge_clobber($arrNewArray[$key], $val);
           }
           else {
               $arrNewArray[$key] = $val;
           }
       }
       else {
           $arrNewArray[$key] = $val;
       }
   }
   return $arrNewArray;
}
?>

Not sure if someone else has already got something similar or better, but this is simple and works for me. :)
03-Sep-2003 05:10
For those who are getting duplicate entries when using this function, there is a very easy solution:

wrap array_unique() around array_merge()

cheers,

k.
tobias_mik at hotmail dot com
25-Jul-2003 07:14
This function merges any number of arrays and maintains the keys:

<?php
function array_kmerge ($array) {
 reset($array);
 while ($tmp = each($array))
 {
  if(count($tmp['value']) > 0)
  {
   $k[$tmp['key']] = array_keys($tmp['value']);
   $v[$tmp['key']] = array_values($tmp['value']);
  }
 }
 while($tmp = each($k))
 {
  for ($i = $start; $i < $start+count($tmp['value']); $i ++)$r[$tmp['value'][$i-$start]] = $v[$tmp['key']][$i-$start];
  $start = count($tmp['value']);
 }
 return $r;
}
?>

<array_merge_recursivearray_multisort>
 Last updated: Thu, 19 May 2005
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