PHP array_merge_recursive() Function

The array_merge_recursive() is an inbuilt function in PHP and is used to merge two or more arrays into a single array recursively. This function is used to merge the elements or values of two or more arrays together into a single array. The merging occurs in such a manner that the values of one array are appended at the end of the previous array. If there are same keys in the given arrays, then the key is assigned a value which has an array that consists of the values with the same key.

Note: The function is different from array_merge() in a way that in case of multiple arrays with same keys, array_merge() function takes the last array value from all the arrays, but in array_merge_recursive() the key is assigned an array which consists of all the values of arrays which has the same key.

Syntax:

array_merge_recursive($array1, $array2, $array3...$arrayn)

Parameters: The function can take any number of arrays as parameter separated by comma (,) that we need to merge. The first parameter $array1 is mandatory.

Return Value: The function returns a merged array which has all the arrays merged. The merging occurs in such a manner that the values of one array are appended at the end of the previous array. If there are same keys in the given arrays, then that key in the output array is assigned an array that consists of the values with the same key.

Examples:

Input : $a1=array("a"=>"raj", "b"=>"striver");
        $a2=array("z"=>"geeks", "b"=>"articles");
Output : 
Array
(
    [a] => raj
    [b] => Array
        (
            [0] => striver
            [1] => articles
        )

    [z] => geeks
)
Explanation: "striver" and "articles" has the same 
key "b", so the key b is assigned to an array which has 
"striver" and "articles" as elements. 

Input :$a1=array("a"=>"raj", "b"=>"striver");
       $a2=array("z"=>"geeks", "d"=>"articles");
Output :
Array
(
    [a] => raj
    [b] => striver
    [z] => geeks
    [d] => articles
)

Below programs illustrate the array_merge_recursive() function:

Program 1: PHP program to demonstrate array_merge_recursive()
function with all different keys.

<?php
// PHP program to demonstrate array_merge_recursive()
// function with same keys
$a1=array("a"=>"raj", "b"=>"striver");
$a2=array("z"=>"geeks", "d"=>"articles");

print_r(array_merge_recursive($a1, $a2));
?>

Output:

Array
(
    [a] => raj
    [b] => striver
    [z] => geeks
    [d] => articles
)

Program 2: PHP program to demonstrate array_merge_recursive() function with same keys.

<?php
// PHP program to demonstrate array_merge_recursive()
// function with same keys
$a1=array("a"=>"raj", "b"=>"striver");
$a2=array("z"=>"geeks", "b"=>"articles");

//function call
print_r(array_merge_recursive($a1, $a2));
?>

Output:

Array
(
    [a] => raj
    [b] => Array
        (
            [0] => striver
            [1] => articles
        )

    [z] => geeks
)

Reference:
http://php.net/manual/en/function.array-merge-recursive.php