array_merge

(PHP 4, PHP 5, PHP 7)

array_merge — 合并一个或多个数组

说明

array_merge ( array $array1 [, array $... ] ) : array

array_merge() 将一个或多个数组的单元合并起来，一个数组中的值附加在前一个数组的后面。返回作为结果的数组。

如果输入的数组中有相同的字符串键名，则该键名后面的值将覆盖前一个值。然而，如果数组包含数字键名，后面的值将不会覆盖原来的值，而是附加到后面。

如果只给了一个数组并且该数组是数字索引的，则键名会以连续方式重新索引。

参数

array1

要合并的第一个数组。

...

要合并的数组列表。

返回值

返回结果数组。

范例

Example #1 array_merge() 例子

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

以上例程会输出：

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

Example #2 Simple array_merge() 例子

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

别忘了数字键名将会被重新编号！ 

Array
(
    [0] => data
)

如果你想完全保留原有数组并只想新的数组附加到后面，用 + 运算符：

<?php
$array1 = array(0 => 'zero_a', 2 => 'two_a', 3 => 'three_a');
$array2 = array(1 => 'one_b', 3 => 'three_b', 4 => 'four_b');
$result = $array1 + $array2;
var_dump($result);
?>

第一个数组的键名将会被保留。在两个数组中存在相同的键名时，第一个数组中的同键名的元素将会被保留，第二个数组中的元素将会被忽略 

array(5) {
  [0]=>
  string(6) "zero_a"
  [2]=>
  string(5) "two_a"
  [3]=>
  string(7) "three_a"
  [1]=>
  string(5) "one_b"
  [4]=>
  string(6) "four_b"
}

Example #3 array_merge() 合并非数组的类型

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

以上例程会输出：

    Array
    (
        [0] => foo
        [1] => bar
    )

参见

User Contributed Notes

souzacomprog at gmail dot com 18-Dec-2019 11:42
Sometimes we need to traverse an array and group / merge the indexes so that it is easier to extract them so that they are related in the iteration.

<?php

$people = [
    ['id' => 1, 'name' => 'Hayley'],
    ['id' => 2, 'name' => 'Jack', 'dad' => 1],
    ['id' => 3, 'name' => 'Linus', 'dad' => 4],
    ['id' => 4, 'name' => 'Peter'],
    ['id' => 5, 'name' => 'Tom', 'dad' => 4],
];

// We set up an array with just the children
function children($dad, $people)
{
    $children = [];
    foreach ($people as $p) {
        if (!empty($p["dad"]) && $p["dad"] == $dad["id"]) {
            $children[] = $p;
        }
    }

    return $children;
}

$family = [];

// We merge each child with its respective parent
foreach ($people as $p) {
    $children = children($p, $people);
    if ($children != []) {
        $family[] = array_merge($p, ["children" => $children]);
    }
}

print_r($family);

?>

//OUTPUT

Array
(
    [0] => Array
        (
            [id] => 1
            [name] => Hayley
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 2
                            [name] => Jack
                            [dad] => 1
                        )

                )

        )

    [1] => Array
        (
            [id] => 4
            [name] => Peter
            [children] => Array
                (
                    [0] => Array
                        (
                            [id] => 3
                            [name] => Linus
                            [dad] => 4
                        )

                    [1] => Array
                        (
                            [id] => 5
                            [name] => Tom
                            [dad] => 4
                        )

                )

        )

)
ousseni dot work at gmail dot com 09-Dec-2019 01:55
A good function to merge by keys

/**
* @param $array1....$arrayn
*/
public function array_merge_keys(){
     $args = func_get_args();
     $result = array();
     foreach($args as $array)
     {
            foreach($array as $key=>$value)
            {
                $result[$key] = $value;
            }
        }
     return $result;
}
makjoybd [at] gmail [dot] com 22-Jul-2019 08:25
$a = array(1,2,3);    // an array
$b = 5;  // anything but not an array

$c = array_merge($a, $b); // shows a PHP warning: Argument #2 is not an array

var_dump($c); // output as NULL

// now merge in reverse order
$d = array_merge($b, $a); // shows a PHP warning: Argument #1 is not an array

var_dump($d); // output as NULL

NOTE: For any operation that relies on the previous array merge operation it is highly necessary to check the arguments as well as the result of the merge are arrays before continuing  as the warning would not stop the operation and this might result in data loss and what not... and this should also be stated in the .documentation. Example #3 somewhat started to demonstrate this but used type casting which made this irrelevant to this matter.
pike-common at kw dot nl 08-Oct-2018 01:49
When mixing string keys and numeric keys, numeric keys are still renumbered after merge.

<?php
        $test1= array("foo"=>"rfoo1",2=>"r21","bar"=>"rbar1");
        $test2= array("foo"=>"rfoo2",2=>"r22","bar"=>"rbar2");
        var_dump(array_merge($test1,$test2));
?>
  array(4) {
    ["foo"]=>
    string(5) "rfoo2"
    [0]=>
    string(3) "r21"
    ["bar"]=>
    string(5) "rbar2"
    [1]=>
    string(3) "r22"
 }

adding arrays doesn't:

<?php
        var_dump($test2+$test1);
?>
  array(3) {
    ["foo"]=>
    string(5) "rfoo2"
    [2]=>
    string(3) "r22"
    ["bar"]=>
    string(5) "rbar2"
  }
withtvpeter at gmail dot com 21-Apr-2018 09:42
Suffice to add, array_merge() creates a new array from the supplied array(s) and does not modify the supplied array(s). Example:

$array1 = ["a" => "one", "b"=>"two"];
$array2 = [ "c" => "three", "d" => "four"];

$mergedArray = array_merge($array1, $array2);

print_r($mergedArray); // => ["a"=> "one", "b"=> "two", "c"=>"three", "d"=>"four"];
print_r($array1);  //=> ["a"=>"one", "b"=>"two"];
matias dot r dot ventura at gmail dot com 06-Apr-2018 06:44
Note that if you want to append one array to another, using a foreach in conjuction with array_push is A LOT faster:

<?php

$array = array("one", "two", "three", "four");
$test1 = array();
$test2 = array();
$mctime = microtime(true);

for($i = 0; $i < 10000; $i++){
    $test1 = array_merge($test1, $array);
}

echo("Test 1: ". (microtime(true) - $mctime) ."s     ");
$mctime = microtime(true);

for($i = 0; $i < 10000; $i++){
    foreach($array as $value){
        array_push($test2, $value);
    }
}

echo("Test 2: ". (microtime(true) - $mctime) ."s     ");
?>

This in my case resolves to:

Test 1: 2.7962880134583s
Test 2: 0.0039298534393311s
ian_channing at hotmail dot com 12-Oct-2017 05:36
array_merge is the equivalent of concat in other languages. I tried to submit a bug that array_concat should be created as an alias to this but it was rejected on the basis they didn't want to polute the namespace and that the documentation should be updated instead. So here's what I put in the bug #73576:

There is no documented array concatenation function. This is a very common function, e.g. Javascript and Ruby have the `concat` function, Python has `+` and Haskell has `++`.

The `array_merge` function is what has be used if you want to concatenate arrays. However it is not mentioned in the documentation (not even in the comments) of that method that that is what should be used.

I propose that `array_concat` be created as an alias of `array_merge`. The concatenation of an associative array is also consistent with trying to merge the hash maps. For example there is a Stack Overflow question on 'concatenating two dictionaries' that is marked as a duplicate of the function 'How to merge two Python dictionaries'. That is, it is consistent that hash map concatenation is the same as hash map merging.

So I believe that `array_concat` is a perfect alias for `array_merge` in terms of numeric arrays and a valid (albeit unnecessary) alias for associative arrays.

This will help almost all developers coming to PHP from other dynamic languages.
titum at lavache dot com 01-Aug-2017 11:56
foreach loop is faster than array_merge to append values to an existing array, so choose the loop instead if you want to add an array to the end of another.

<?php
// Create an array of arrays
$chars = [];
for ($i = 0; $i < 15000; $i++) {
    $chars[] = array_fill(0, 10, 'a');
}

// test array_merge
$new = [];
$start = microtime(TRUE);
foreach ($chars as $splitArray) {
    $new = array_merge($new, $splitArray);
}
echo microtime(true) - $start; // => 14.61776 sec

// test foreach
$new = [];
$start = microtime(TRUE);
foreach ($chars as $splitArray) {
    foreach ($splitArray as $value) {
        $new[] = $value;
    }
}
echo microtime(true) - $start; // => 0.00900101 sec
// ==> 1600 times faster
?>
woodongwong at gmail dot com 26-Apr-2017 09:35
As PHP 5.6 you can use array_merge + "splat" operator to reduce a bidimensonal array to a simple array:

<?php
$data = [[1, 2], [3], [4, 5]];
    print_r(array_merge(... $data)); // [1, 2, 3, 4, 5];
?>

PHP < 5.6:

<?php
$data = [[1, 2], [3], [4, 5]];
print_r(array_reduce($data, 'array_merge', []));   // [1, 2, 3, 4, 5];

?>
padina 10-Apr-2017 08:10
Static functions of Classes  with Namespace are callables too.

namespace Vendor\Extension\Service;

class SvgFormationService implements \TYPO3\CMS\Core\SingletonInterface
{

    public static function doubleQuote($value) {
        return '"'.$value.'"';
    }

    public static function otherFunc ($value) {
        $tagAttributes = array_map('\Vendor\Extension\Service\SvgFormationService::doubleQuote',$tagAttributes);
    }
}
rameezsoomro dot pk at live dot com 17-Jan-2017 05:17
Array merge will return null if any parameter not an array
<?php
$DB_user_result=  DB::select()->where()->get(); // return null if not found.
$DB_exists_user_info = ['name'=>'Rameez Soomro','Location'=>'Karachi, Sindh, Pakistan'];
print_r(array_merge($DB_user_result, $DB_exists_user_info));  //NULL
?>
Here is function for solution of array_merge
function copied from  http://sdtuts.com/php-array_merge-function-issue/
<?php
function merge_arrays_obj(){
  $func_info = debug_backtrace();
  $func_args = $func_info[0]['args'];
  $return_array_data = array();
  foreach($func_args as $args_index=>$args_data){
    if(is_array($args_data) || is_object($args_data)){
    $return_array_data = array_merge($return_array_data,$args_data);
    }
  }
  return $return_array_data;
}
?>

Code example how to use it
<?php
$array = array('abc'=>'abcparam');
$null_array = null;
$new_arraydata = array('username'=>'Rameez Soomro','usersite'=>'http://sdtuts.com');
$new_arrayOBJ = array ( (object) array('obj_DATA' => 'ABC_OBJ','obj_next_index '=>'ABC_OBJ_NEXT_INDEX') );
$new_array_data = merge_arrays_obj($array,$null_array,$new_arraydata,$new_arrayOBJ);
print_r($new_array_data);
?>
jcmarchi at gmail dot comfive 20-May-2016 04:06
It is not officially documented but it is summarily important information for everyone to know: neither array_merge or array_merge_recursive functions will function correctly if non-array objects  are used as parameters.

You would probably expect these functions to ignore non-array elements, right? However, if one parameter is null it PHP will not only return null for the entire function but will also (not always) raise an error, such as :

    [ Warning: array_merge(): Argument #x is not an array... ]

This error message won't appear if the defective variable is an empty array (an empty array is still an array), but it will result in an undesirable incomplete Array.

There are several solutions for this problem by validating the Arrays before use them in these functions, but the most efficient way is to enforce the element as an array directly in the function itself. I.e.:

$merged = array_merge( (array)$first_array, (array)$second_array );
arifulin at gmail dot com 15-Mar-2016 09:10
public function mergeArrays($arrays, $field)
    {
        //take array in arrays for retrive structure after merging
        $clean_array = current($arrays);
        foreach ($clean_array as $i => $value) {
            $clean_array[$i]='';
        }

        $merged_array = [];
        $name = '';
        foreach ($arrays as $array){
            $array = array_filter($array); //clean array from empty values
            if ($name == $array[$field]) {
                $merged_array[$name] = array_merge($merged_array[$name], $array);
                $name = $array[$field];
            } else {
                $name = $array[$field];
                $merged_array[$name] = $array;
            }
        }
        //have to be cleaned from array 'field' signs to return original structure of arrays
        foreach ($merged_array as $array){
            $ready_array[] = array_merge($clean_array, $array);
        }

        return $ready_array;
    }
kristopolous at yahoo dot com 26-Feb-2016 10:46
I constantly forget the direction of array_merge so this is partially for me and partially for people like me.

array_merge is a non-referential non-inplace right-reduction. For different ctrl-f typers, it's reduce-right, side-effect free, idempotent, and non in-place.

ex:

$a = array_merge(['k' => 'a'], ['k' => 'b']) => ['k' => 'b']
array_merge(['z' => 1], $a) => does not modify $a but returns ['k' => 'b', 'z' => 1];

Hopefully this helps people that constant look this up such as myself.
info at eastghost dot com 05-Sep-2015 01:37
We noticed array_merge is relatively slower than manually extending an array:

given:
$arr_one[ 'x' => 1, 'y' => 2 ];
$arr_two[ 'a' => 10, 'b' => 20 ];

the statement:
$arr_three = array_merge( $arr_one, $arr_two );
is routinely 200usec slower than:

$arr_three = $arr_one;
foreach( $arr_two as $k => $v ) { $arr_three[ $k ] = $v; }

200usec didn't matter...until we started combining huge arrays.

PHP 5.6.x
Anonymous 29-Jun-2015 09:48
As PHP 5.6 you can use array_merge + "splat" operator to reduce a bidimensonal array to a simple array:

<?php
$data = [[1, 2], [3], [4, 5]];
print_r(array_merge(... $data)); // [1, 2, 3, 4, 5];
?>
gj@php 01-Jul-2014 02:59
i did a small benchmark (on  PHP 5.3.3) comparing:
* using array_merge on numerically indexed arrays
* using a basic double loop to merge multiple arrays

the performance difference is huge:

<?php

require_once("./lib/Timer.php");

function method1($mat){
    $all=array();
    foreach($mat as $arr){
        $all=array_merge($all,$arr);
    }
    return $all;
}

function method2($mat){
    $all=array();
    foreach($mat as $arr){
        foreach($arr as $el){
            $all[]=$el;
        }
    }
    return $all;
}

function tryme(){
    $y=250; //#arrays
    $x=200; //size per array
    $mat=array();
    //build big matrix
    for($i=0;$i<$y;$i++){
        for($j=0;$j<$x;$j++){
            $mat[$i][$j]=rand(0,1000);
        }   
    }

    $t=new Timer();
    method1($mat);
    $t->displayTimer();
   
    $t=new Timer();
    method2($mat);
    $t->displayTimer();
   
/*
output:
Script runtime: 2.36782 secs. Script runtime: 0.02137 sec.
*/
   
}

tryme();

?>

So that's more than a factor 100!!!!!
Angel I 12-Jun-2014 01:57
An addition to what Julian Egelstaff above wrote - the array union operation (+) is not doing an array_unique - it will just not use the keys that are already defined in the left array.  The difference between union and merge can be seen in an example like this:

<?php
$arr1['one'] = 'one';
$arr1['two'] = 'two';

$arr2['zero'] = 'zero';
$arr2['one'] = 'three';
$arr2['two'] = 'four';

$arr3 = $arr1 + $arr2;
var_export( $arr3 );
# array ( 'one' => 'one', 'two' => 'two', 'zero' => 'zero', )

$arr4 = array_merge( $arr1, $arr2 );
var_export( $arr4 );
# array ( 'one' => 'three', 'two' => 'four', 'zero' => 'zero', )
?>
php at metehanarslan dot com 10-Jun-2014 10:49
Sometimes you need to modify an array with another one here is my approach to replace an array's content recursively with delete opiton. Here i used "::delete::" as reserved word to delete items.

<?php
$person= array(
    "name" => "Metehan",
    "surname"=>"Arslan",
    "age"=>27,
    "mail"=>"hidden",
    "favs" => array(
        "language"=>"php",
        "planet"=>"mercury",
        "city"=>"istanbul")
);

$newdata = array(
    "age"=>28,
    "mail"=>"::delete::",
    "favs" => array(
        "language"=>"js",
        "planet"=>"mercury",
        "city"=>"shanghai")
);

print_r(array_overlay($person,$newdata));
// result: Array ( [name] => Metehan [surname] => Arslan [age] => 28 [favs] => Array ( [language] => js [planet] => mercury [city] => shanghai ) )

function array_overlay($a1,$a2)
{
    foreach($a1 as $k => $v) {
        if ($a2[$k]=="::delete::"){
            unset($a1[$k]);
            continue;
        };
        if(!array_key_exists($k,$a2)) continue;
        if(is_array($v) && is_array($a2[$k])){
            $a1[$k] = array_overlay($v,$a2[$k]);
        }else{
            $a1[$k] = $a2[$k];
        }
       
    }
    return $a1;
}
?>
rajaimranqamer at gmail dot com 28-May-2014 08:26
to get unique value from multi dimensional array use this instead of array_unique(), because array_unique() does not work on multidimensional:
array_map("unserialize", array_unique(array_map("serialize", $array)));
Hope this will help someone;
Example
$a=array(array('1'),array('2'),array('3'),array('4));
$b=array(array('2'),array('4'),array('6'),array('8));
$c=array_merge($a,$b);
then write this line to get unique values
$c=array_map("unserialize", array_unique(array_map("serialize", $c)));
print_r($c);
vladas dot dirzys at gmail dot com 21-Aug-2013 09:11
To combine several results (arrays):

<?php
$results = array(
    array(
        array('foo1'),
        array('foo2'),
    ),
    array(
        array('bar1'),
        array('bar2'),
    ),
);

$rows = call_user_func_array('array_merge', $results);
print_r($rows);
?>

The above example will output:

Array
(
    [0] => Array
        (
            [0] => foo1
        )

    [1] => Array
        (
            [0] => foo2
        )

    [2] => Array
        (
            [0] => bar1
        )

    [3] => Array
        (
            [0] => bar2
        )

)

However, example below helps to preserve numeric keys:

<?php
$results = array(
    array(
        123 => array('foo1'),
        456 => array('foo2'),
    ),
    array(
        321 => array('bar1'),
        654 => array('bar2'),
    ),
);

$rows = array();
foreach ($results as &$result) {
    $rows = $rows + $result; // preserves keys
}
print_r($rows);
?>

The above example will output:
Array
(
    [123] => Array
        (
            [0] => foo1
        )

    [456] => Array
        (
            [0] => foo2
        )

    [321] => Array
        (
            [0] => bar1
        )

    [654] => Array
        (
            [0] => bar2
        )
)
Gemorroj 14-May-2012 08:37
The function behaves differently with numbers more than PHP_INT_MAX
<?php
$arr1 = array('1234567898765432123456789' => 'dd');
$arr2 = array('123456789876543212345678' => 'ddd', '35' => 'xxx');
var_dump(array_merge($arr1, $arr2));
//
$arr1 = array('1234' => 'dd');
$arr2 = array('12345' => 'ddd', '35' => 'xxx');
var_dump(array_merge($arr1, $arr2));
?>
result:
array(3) {
  ["1234567898765432123456789"]=>
  string(2) "dd"
  ["123456789876543212345678"]=>
  string(3) "ddd"
  [0]=>
  string(3) "xxx"
}
array(3) {
  [0]=>
  string(2) "dd"
  [1]=>
  string(3) "ddd"
  [2]=>
  string(3) "xxx"
}
alejandro dot anv at gmail dot com 20-Feb-2012 11:26
WARNING: numeric subindexes are lost when merging arrays.

Check this example:

$a=array('abc'=>'abc','def'=>'def','123'=>'123','xyz'=>'xyz');
echo "a=";print_r($a);
$b=array('xxx'=>'xxx');
echo "b=";print_r($b);
$c=array_merge($a,$b);
echo "c=";print_r($c);

The result is this:

c=Array
(
    [abc] => abc
    [def] => def
    [0] => 123
    [xyz] => xyz
    [xxx] => xxx
)
w_barath at hotmail dot com 04-Oct-2011 04:42
I keep seeing posts for people looking for a function to replace numeric keys.

No function is required for this, it is default behavior if the + operator:

<?php
$a=array(1=>"one", "two"=>2);
$b=array(1=>"two", "two"=>1, 3=>"three", "four"=>4);

print_r($a+$b);
?>

Array
(
    [1] => one
    [two] => 2
    [3] => three
    [four] => 4
)

How this works:

The + operator only adds unique keys to the resulting array.  By making the replacements the first argument, they naturally always replace the keys from the second argument, numeric or not! =)
craig ala craigatx.com 26-Oct-2010 10:25
Reiterating the notes about casting to arrays, be sure to cast if one of the arrays might be null:

<?php
header("Content-type:text/plain");
$a = array('zzzz', 'xxxx');
$b = array('mmmm','nnnn');

echo "1 ==============\r\n";
print_r(array_merge($a, $b));

echo "2 ==============\r\n";
$b = array();
print_r(array_merge($a, $b));

echo "3 ==============\r\n";
$b = null;
print_r(array_merge($a, $b));

echo "4 ==============\r\n";
$b = null;
print_r(array_merge($a, (array)$b));

echo "5 ==============\r\n";
echo is_null(array_merge($a, $b)) ? 'Result is null' : 'Result is not null';
?>

Produces:

1 ==============
Array
(
    [0] => zzzz
    [1] => xxxx
    [2] => mmmm
    [3] => nnnn
)
2 ==============
Array
(
    [0] => zzzz
    [1] => xxxx
)
3 ==============
4 ==============
Array
(
    [0] => zzzz
    [1] => xxxx
)
5 ==============
Result is null
zagadka at evorg dot dk 20-Aug-2010 05:54
Note that if you use + to merge array in order to preserve keys, that in case of duplicates the values from the left array in the addition is used.
Tudor 27-Sep-2009 01:10
array_merge will merge numeric keys in array iteration order, not in increasing numeric order. For example:

<?php
$a = array(0=>10, 1=>20);  // same as array(10, 20);
$b = array(0=>30, 2=>50, 1=>40);
?>

array_merge($a, $b) will be array(10, 20, 30, 50, 40) and not array(10, 20, 30, 40, 50).
Julian Egelstaff 30-Jul-2009 11:48
In some situations, the union operator ( + ) might be more useful to you than array_merge.  The array_merge function does not preserve numeric key values.  If you need to preserve the numeric keys, then using + will do that.

ie:

<?php

$array1[0] = "zero";
$array1[1] = "one";

$array2[1] = "one";
$array2[2] = "two";
$array2[3] = "three";

$array3 = $array1 + $array2;

//This will result in::

$array3 = array(0=>"zero", 1=>"one", 2=>"two", 3=>"three");

?>

Note the implicit "array_unique" that gets applied as well.  In some situations where your numeric keys matter, this behaviour could be useful, and better than array_merge.

--Julian
enaeseth at gmail dot com 20-Jul-2009 02:27
In both PHP 4 and 5, array_merge preserves references in array values. For example:

<?php
$foo = 12;
$array = array("foo" => &$foo);
$merged_array = array_merge($array, array("bar" => "baz"));
$merged_array["foo"] = 24;
assert($foo === 24); // works just fine
?>
carrox at inbox dot lv 31-Aug-2008 04:41
Usage of operand '+' for merging arrays:

<?php

$a=array(
'a'=>'a1',
'b'=>'a2',
'a3',
'a4',
'a5');

$b=array('b1',
'b2',
'a'=>'b3',
'b4');

$a+=$b;

print_r($a);

?>

output:
Array
(
    [a] => a1
    [b] => a2
    [0] => a3
    [1] => a4
    [2] => a5
    [3] => b5
)

numeric keys of elements of array B what not presented in array A was added.

<?php

$a=array('a'=>'a1','b'=>'a2','a3','a4','a5');
$b=array(100=>'b1','b2','a'=>'b3','b4');

$a+=$b;

print_r($a);

?>

output:

   [a] => a1
    [b] => a2
    [0] => a3
    [1] => a4
    [2] => a5
    [100] => b1
    [101] => b2
    [102] => b4

autoindex for array B started from 100, these keys not present in array A, so this elements was added to array A
ron at ronfolio dot com 11-Aug-2008 06:44
I needed a function similar to ian at fuzzygroove's array_interlace, but I need to pass more than two arrays.

Here's my version, You can pass any number of arrays and it will interlace and key them properly.

<?php
function array_interlace() {
    $args = func_get_args();
    $total = count($args);

    if($total < 2) {
        return FALSE;
    }
   
    $i = 0;
    $j = 0;
    $arr = array();
   
    foreach($args as $arg) {
        foreach($arg as $v) {
            $arr[$j] = $v;
            $j += $total;
        }
       
        $i++;
        $j = $i;
    }
   
    ksort($arr);
    return array_values($arr);
}
?>

Example usage:
<?php
$a = array('a', 'b', 'c', 'd');
$b = array('e', 'f', 'g');
$c = array('h', 'i', 'j');
$d = array('k', 'l', 'm', 'n', 'o');

print_r(array_interlace($a, $b, $c, $d));
?>

result:

Array
(
    [0] => a
    [1] => e
    [2] => h
    [3] => k
    [4] => b
    [5] => f
    [6] => i
    [7] => l
    [8] => c
    [9] => g
    [10] => j
    [11] => m
    [12] => d
    [13] => n
    [14] => o
)

Let me know if you improve on it.
bishop 04-Apr-2008 02:02
The documentation is a touch misleading when it says: "If only one array is given and the array is numerically indexed, the keys get reindexed in a continuous way."  Even with two arrays, the resulting array is re-indexed:

[bishop@predator staging]$ cat array_merge.php
<?php
$a = array (23 => 'Hello', '42' => 'World');
$a = array_merge(array (0 => 'I say, '), $a);
var_dump($a);
?>
[bishop@predator staging]$ php-5.2.5 array_merge.php
array(3) {
  [0]=>
  string(7) "I say, "
  [1]=>
  string(5) "Hello"
  [2]=>
  string(5) "World"
}
[bishop@predator staging]$ php-4.4.7 array_merge.php
array(3) {
  [0]=>
  string(7) "I say, "
  [1]=>
  string(5) "Hello"
  [2]=>
  string(5) "World"
}
Hayley Watson 04-Nov-2007 12:38
As has already been noted before, reindexing arrays is most cleanly performed by the array_values() function.
clancyhood at gmail dot com 21-Jul-2007 04:52
Similar to Jo I had a problem merging arrays (thanks for that Jo you kicked me out of my debugging slumber) - array_merge does NOT act like array_push, as I had anticipated

<?php

$array = array('1', 'hello');
array_push($array, 'world');

var_dump($array);

// gives '1', 'hello', 'world'

 
$array = array('1', 'hello');
array_merge($array, array('world'));

// gives '1', 'hello'

$array = array('1', 'hello');
$array = array_merge($array, array('world'));

// gives '1', 'hello', 'world'

?>

hope this helps someone
Joe at neosource dot com dot au 03-Jun-2007 11:51
I found the "simple" method of adding arrays behaves differently as described in the documentation in PHP v5.2.0-10.

$array1 + $array2 will only combine entries for keys that don't already exist.

Take the following example:

$ar1 = array('a', 'b');
$ar2 = array('c', 'd');
$ar3 = ($ar1 + $ar2);
print_r($ar3);

Result:

Array
(
    [0] => a
    [1] => b
)

Where as:

$ar1 = array('a', 'b');
$ar2 = array('c', 'd');
$ar3 = array_merge($ar1, $ar2);
print_r($ar3);

Result:

Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
)

Hope this helps someone.
RQuadling at GMail dot com 21-May-2007 05:05
For asteddy at tin dot it and others who are trying to merge arrays and keep the keys, don't forget the simple + operator.

Using the array_merge_keys() function (with a small mod to deal with multiple arguments), provides no difference in output as compared to +.

<?php
$a = array(-1 => 'minus 1');
$b = array(0 => 'nought');
$c = array(0 => 'nought');
var_export(array_merge_keys($a,$b));
var_export($a + $b);
var_export(array_merge_keys($a,$b,$c));
var_export($a + $b + $c);
?>

results in ...

array (  -1 => 'minus 1',  0 => 'nought',)
array (  -1 => 'minus 1',  0 => 'nought',)
array (  -1 => 'minus 1',  0 => 'nought',)
array (  -1 => 'minus 1',  0 => 'nought',)
BigueNique at yahoo dot ca 28-Sep-2006 07:10
Needed an quick array_merge clone that preserves the keys:

<?php
// function array_join
// merges 2 arrays preserving the keys,
// even if they are numeric (unlike array_merge)
// if 2 keys are identical, the last one overwites
// the existing one, just like array_merge
// merges up to 10 arrays, minimum 2.
function array_join($a1, $a2, $a3=null, $a4=null, $a5=null, $a6=null, $a7=null, $a8=null, $a9=null, $a10=null) {
    $a=array();
    foreach($a1 as $key=>$value) $a[$key]=$value;
    foreach($a2 as $key=>$value) $a[$key]=$value;
    if (is_array($a3)) $a=array_join($a,$a3,$a4,$a5,$a6,$a7,$a8,$a9,$a10);
    return $a;
}
?>
kaigillmann at gmxpro dot net 02-Nov-2005 03:56
If you need to merge two arrays without having multiple entries, try this:

<?php
function array_fusion($ArrayOne, $ArrayTwo)
{
    return array_unique(array_merge($ArrayOne, $ArrayTwo));
}
?>
ntpt at centrum dot cz 14-Jul-2005 06:44
Old behavior of array_merge can be restored by simple  variable type casting like this

array_merge((array)$foo,(array)$bar);

works good in php 5.1.0 Beta 1, not tested in other versions

seems that empty or not set variables are casted to empty arrays
Alec Solway 20-Jan-2005 10:05
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.
Frederick.Lemasson{AT}kik-it.com 23-Dec-2004 02:57
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
)

?>
bcraigie at bigfoot dot com 24-Aug-2004 12:37
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.
frankb at fbis dot net 25-Feb-2004 04:02
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.
loner at psknet dot !NOSPAM!com 29-Sep-2003 03:00
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.
03-Sep-2003 03:10
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 05:14
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;
}
?>