array_merge

(PHP 4, PHP 5, PHP 7, PHP 8)

array_mergeMerge one or more arrays

Description

array_merge(array ...$arrays): array

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.

Values in the input arrays with numeric keys will be renumbered with incrementing keys starting from zero in the result array.

Parameters

arrays

Variable list of arrays to merge.

Return Values

Returns the resulting array. If called without any arguments, returns an empty array.

Changelog

Version Description
7.4.0 This function can now be called without any parameter. Formerly, at least one parameter has been required.

Examples

Example #1 array_merge() example

<?php
$array1 
= array("color" => "red"24);
$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(=> "data");
$result array_merge($array1$array2);
?>

Don't forget that numeric keys will be renumbered!

Array
(
    [0] => data
)

If you want to append array elements from the second array to the first array while not overwriting the elements from the first array and not re-indexing, use the + array union operator:

<?php
$array1 
= array(=> 'zero_a'=> 'two_a'=> 'three_a');
$array2 = array(=> 'one_b'=> 'three_b'=> 'four_b');
$result $array1 $array2;
var_dump($result);
?>

The keys from the first array will be preserved. If an array key exists in both arrays, then the element from the first array will be used and the matching key's element from the second array will be ignored.

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() with non-array types

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

The above example will output:

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

See Also

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User Contributed Notes 3 notes

up
268
Julian Egelstaff
12 years ago
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
up
6
fsb at thefsb dot org
1 year ago
We no longer need array_merge() as of PHP 7.4.

    [...$a, ...$b]

does the same as

    array_merge($a, $b)

and can be faster too.

https://wiki.php.net/rfc/spread_operator_for_array#advantages_over_array_merge
up
0
Andreas Hofmann
17 days ago
In addition to the text and Julian Egelstaffs comment regarding to keep the keys preserved with the + operator:
When they say "input arrays with numeric keys will be renumbered" they MEAN it. If you think you are smart and put your numbered keys into strings, this won't help. Strings which contain an integer will also be renumbered! I fell into this trap while merging two arrays with book ISBNs as keys. So let's have this example:

<?php
    $test1
['24'] = 'Mary';
   
$test1['17'] = 'John';

   
$test2['67'] = 'Phil';
   
$test2['33'] = 'Brandon';

   
$result1 = array_merge($test1, $test2);
   
var_dump($result1);

   
$result2 = [...$test1, ...$test2];    // mentioned by fsb
   
var_dump($result2);
?>

You will get both:

array(4) {
  [0]=>
  string(4) "Mary"
  [1]=>
  string(4) "John"
  [2]=>
  string(4) "Phil"
  [3]=>
  string(7) "Brandon"
}

Use the + operator or array_replace, this will preserve - somewhat - the keys:

<?php
    $result1
= array_replace($test1, $test2);
   
var_dump($result1);

   
$result2 = $test1 + $test2;
   
var_dump($result2);
?>

You will get both:

array(4) {
  [24]=>
  string(4) "Mary"
  [17]=>
  string(4) "John"
  [67]=>
  string(4) "Phil"
  [33]=>
  string(7) "Brandon"
}

The keys will keep the same, the order will keep the same, but with a little caveat: The keys will be converted to integers.
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