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array_merge
(PHP 4, PHP 5, PHP 7, PHP 8) array_merge — Merge one or more arrays
Description
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 = ["color" => "red", 2, 4];
$array2 = ["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 = [];
$array2 = [1 => "data"];
$result = array_merge($array1, $array2);
print_r($result);
Don't forget that numeric keys will be renumbered!
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 = [0 => 'zero_a', 2 => 'two_a', 3 => 'three_a'];
$array2 = [1 => 'one_b', 3 => 'three_b', 4 => '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"
}
Julian Egelstaff ¶17 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
ChrisM ¶4 years ago
I wished to point out that while other comments state that the spread operator should be faster than array_merge, I have actually found the opposite to be true for normal arrays. This is the case in both PHP 7.4 as well as PHP 8.0. The difference should be negligible for most applications, but I wanted to point this out for accuracy.
Below is the code used to test, along with the results:
<?php
$before = microtime(true);
for ($i=0 ; $i<10000000 ; $i++) {
$array1 = ['apple','orange','banana'];
$array2 = ['carrot','lettuce','broccoli'];
$array1 = [...$array1,...$array2];
}
$after = microtime(true);
echo ($after-$before) . " sec for spread\n";
$before = microtime(true);
for ($i=0 ; $i<10000000 ; $i++) {
$array1 = ['apple','orange','banana'];
$array2 = ['carrot','lettuce','broccoli'];
$array1 = array_merge($array1,$array2);
}
$after = microtime(true);
echo ($after-$before) . " sec for array_merge\n";
?>
PHP 7.4:
1.2135608196259 sec for spread
1.1402177810669 sec for array_merge
PHP 8.0:
1.1952061653137 sec for spread
1.099925994873 sec for array_merge
Andreas Hofmann ¶4 years 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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