PHP array_merge() Function
The array_merge() function merges one or more arrays into one array.
Tip: You can assign one array to the function, or as many as you like.
Note: If two or more array elements have the same key, the last one overrides the others.
Note: If you assign only one array to the array_merge() function, and the keys are integers, the function returns a new array with integer keys starting at 0 and increases by 1 for each value (See example below).
Tip: The difference between this function and the array_merge_recursive() function is when two or more array elements have the same key. Instead of override the keys, the array_merge_recursive() function makes the value as an array.
Syntax
Parameter Values
| Parameter | Description |
|---|---|
| array1 | Required. Specifies an array |
| array2 | Optional. Specifies an array |
| array3. | Optional. Specifies an array |
Technical Details
| Return Value: | Returns the merged array |
|---|---|
| PHP Version: | 4+ |
| Changelog: | As of PHP 5.0, this function only accept parameters of type array |
More Examples
Example
Merge two associative arrays into one array:
Example
Using only one array parameter with integer keys:
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.
Values in the input arrays with numeric keys will be renumbered with incrementing keys starting from zero in the result array.
Parameters
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
$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
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:
$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 );
?>
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
$beginning = ‘foo’ ;
$end = array( 1 => ‘bar’ );
$result = array_merge ((array) $beginning , (array) $end );
print_r ( $result );
?>
The above example will output:
See Also
- array_merge_recursive() — Merge one or more arrays recursively
- array_replace() — Replaces elements from passed arrays into the first array
- array_combine() — Creates an array by using one array for keys and another for its values
- array operators
User Contributed Notes 8 notes
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.
$array1 [ 0 ] = «zero» ;
$array1 [ 1 ] = «one» ;
$array2 [ 1 ] = «one» ;
$array2 [ 2 ] = «two» ;
$array2 [ 3 ] = «three» ;
$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.
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:
for ( $i = 0 ; $i < 10000000 ; $i ++) $array1 = [ 'apple' , 'orange' , 'banana' ];
$array2 = [ ‘carrot’ , ‘lettuce’ , ‘broccoli’ ];
$after = microtime ( true );
echo ( $after — $before ) . » sec for spread\n» ;
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
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:
$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:
Use the + operator or array_replace, this will preserve — somewhat — the keys:
$result1 = array_replace ( $test1 , $test2 );
var_dump ( $result1 );
$result2 = $test1 + $test2 ;
var_dump ( $result2 );
?>
You will get both:
The keys will keep the same, the order will keep the same, but with a little caveat: The keys will be converted to integers.
We no longer need array_merge() as of PHP 7.4.
Not to contradict ChrisM’s test, but I ran their code example and I got very different results for PHP 8.0.
Testing PHP 8.0.14
1.4955070018768 sec for spread
4.4120140075684 sec for array_merge
If you’re trying to merge an array with something that evaluates to NULL, you’ll get unpredictable results:
$c = array_merge ( $a , $b ); // this won’t work
echo «The merged array is:» ;
var_dump ( $c );
?>
Depending on your error setting, you might not even get anything at all.
array(3) [0]=>
string(1) «1»
[1]=>
string(1) «2»
[2]=>
string(1) «4»
>
NULL
PHP Warning: array_merge(): Expected parameter 2 to be an array, null given in /home/gwyneth/stupid-test.php on line 8
The merged array is: NULL
array(3) [0]=>
string(1) «1»
[1]=>
string(1) «2»
[2]=>
string(1) «4»
>
NULL
PHP Fatal error: Uncaught TypeError: array_merge(): Argument #2 must be of type array, null given in /home/gwyneth/stupid-test.php:8
Stack trace:
#0 /home/gwyneth/stupid-test.php(8): array_merge()
#1
thrown in /home/gwyneth/stupid-test.php on line 8
Depending on your display/debug settings, you might not even get anything.
The solution, of course, is to do a quick & dirty test before passing the 2nd argument:
$c = array_merge ( $a , $b ?? []);
echo «The merged array is:» ;
var_dump ( $c );
?>
Which gives the expected result (PHP 7.4 to PHP 8.2):
While it’s perfectly legitimate to merge empty arrays, null is *not* an empty array!
array_merge
Сливает элементы одного или большего количества массивов таким образом, что значения одного массива присоединяются к концу предыдущего. Результатом работы функции является новый массив.
Если входные массивы имеют одинаковые строковые ключи, тогда каждое последующее значение будет заменять предыдущее. Однако, если массивы имеют одинаковые числовые ключи, значение, упомянутое последним, не заменит исходное значение, а будет добавлено в конец массива.
В результирующем массиве значения исходного массива с числовыми ключами будут перенумерованы в возрастающем порядке, начиная с нуля.
Список параметров
Исходный сливаемый массив.
Дополнительные сливаемые массивы.
Возвращаемые значения
Возвращает результирующий массив.
Примеры
Пример #1 Пример использования array_merge()
$array1 = array( «color» => «red» , 2 , 4 );
$array2 = array( «a» , «b» , «color» => «green» , «shape» => «trapezoid» , 4 );
$result = array_merge ( $array1 , $array2 );
print_r ( $result );
?>
Результат выполнения данного примера:
Array ( [color] => green [0] => 2 [1] => 4 [2] => a [3] => b [shape] => trapezoid [4] => 4 )
Пример #2 Простой пример использования array_merge()
Помните, что числовые ключи будут перенумерованы!
Если вы хотите дополнить первый массив элементами второго без перезаписи элементов первого массива и без переиндексации, используйте оператор объединения массивов +:
$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 );
?>
Ключи из первого массива будут сохранены. Если ключ массива существует в обоих массивах, то будет использован элемент из первого массива, а соответствующий элемент из второго массива будет проигнорирован.
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" >
Пример #3 array_merge() с не массивами
$beginning = ‘foo’ ;
$end = array( 1 => ‘bar’ );
$result = array_merge ((array) $beginning , (array) $end );
print_r ( $result );
?>
Результат выполнения данного примера:
Смотрите также
- array_merge_recursive() — Рекурсивное слияние двух или более массивов
- array_replace() — Замена элементов массива элементами других переданных массивов
- array_combine() — Создает новый массив, используя один массив в качестве ключей, а другой в качестве соответствующих значений
- array operators