PHP: Remove parent array and merge the lower arrays into one array

Example of array

$arr = [
    [0] => Array
        (
            [attribute_color] => blue
        )
    [1] => Array
        (
                  [attribute_width] => 100
)
]

to:

Array
    (
            [attribute_color] => blue
                  [attribute_width] => 100
    )

Here you can use this short PHP function. It works as soon as the upper array is number-indexed, as in the example shown.

$flat = call_user_func_array('array_merge', $arr);