Sorting Deep Multidimentional array PHP

Given the following array:

Array 
(
    [0] => Array
        (
            [0] => Array
                (
                    [key1] => var1
                    [key2] => var2
                    [sortOnMe] => 4
                )

            [1] => N/A
            [2] => N/A
            [3] => N/A
        )

    [1] => Array
        (
            [0] => Array
                (
                    [key1] => var1
                    [key2] => var2
                    [sortOnMe] => 2
                )

            [1] => N/A
            [2] => N/A
            [3] => N/A
        )
)

Given the following array: Array ( [0] => Array ( [0] => Array ( [key1] => var1 [key2] => var2 [sortOnMe] => 4 ) [1] => N/A [2] => N/A [3] => N/A ) [1] => Array ( [0] => Array ( [key1] => var1 [key2] => var2 [sortOnMe] => 2 ) [1] => N/A [2] => N/A [3] => N/A ) ) How can I sort this array considering the key I want is deep in the structure? I assume usort but not sure what to pass into the function?

Ans:

usort($arr, "mysortfunc");

function mysortfunc($a, $b)
{
    if ($a[0]['sortOnMe'] == $b[0]['sortOnMe'])
    {
        return 0;
    }
    else
    {
        return ($a[0]['sortOnMe'] < $b[0]['sortOnMe']) ? -1 : 1;
    }
}