Merge multiple arrays using PHP array_merge() function

PHP array_merge() function is a built-in function for merging multiple arrays. This function can combine multiple arrays into a new array. In this article, we will discuss how to merge multiple arrays using PHP array_merge() function.

How to use the PHP array_merge() function

The PHP array_merge() function has many uses, but the most common use is to merge two or more groups into one. The following is a simple example:

$array1 = array('a', 'b', 'c');
$array2 = array('d', 'e', 'f');
$result = array_merge($array1, $array2);
print_r($result);

Output the following results:

Array ( [0] => a [1] => b [2] => c [3] => d [4] => e [5] => f )

In the above example, we merged the two arrays $array1 and $array2 into a new array $result. This new array contains all elements of the two original arrays.

Details of using the PHP array_merge() function

When using the PHP array_merge() function, there are several details to pay attention to:

1. If the merged array Contains the same key name (i.e. array subscript), then the subsequent key value will overwrite the previous key value. For example:

$array1 = array('a' => 1, 'b' => 2);
$array2 = array('b' => 3, 'c' => 4);
$result = array_merge($array1, $array2);
print_r($result);

The output is as follows:

Array ( [a] => 1 [b] => 3 [c] => 4 )

In the above example, the $b key name in the array $array2 overwrites the $b key name in the array $array1, so The final result is 3 instead of 2. The $a key name in array $array1 and the $c key name in array $array2 are retained.

2. If the array to be merged is an associative array (that is, an array containing non-numeric key names), then the PHP array_merge() function will re-index the array. This means that the original key names will be ignored and the new array will be numerically indexed. For example:

$array1 = array('a' => 1, 'b' => 2);
$array2 = array('c' => 3, 'd' => 4);
$result = array_merge($array1, $array2);
print_r($result);

Output the following results:

Array ( [a] => 1 [b] => 2 [c] => 3 [d] => 4 )

In the above example, the arrays $array1 and $array2 are both associative arrays. When they are merged, the PHP array_merge() function creates a new array and assigns them new key names using numerical indexes. The original key name is ignored.

3. If the array to be merged contains other arrays, these arrays will be merged recursively. For example:

$array1 = array('a' => array('b' => 1, 'c' => 2));
$array2 = array('a' => array('d' => 3, 'e' => 4));
$result = array_merge($array1, $array2);
print_r($result);

Output the following results:

Array ( [a] => Array ( [b] => 1 [c] => 2 [d] => 3 [e] => 4 ) )

In the above example, the arrays $array1 and $array2 both contain a subarray named $a. When they are merged, the PHP array_merge() function will merge them recursively and create a new subarray. In the final result, the new subarray contains the original $b, $c, $d, and $e key values.

Summary

PHP array_merge() function is a very useful array function that can merge multiple arrays into one. We can use it to merge numeric or associative arrays, and we can also use it to merge multiple subarrays recursively. However, when using this function, we need to pay attention to some details to avoid unexpected results.

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