I have written this function so its sort an multidimensional array with a specific key.

<?php
function sort_array($array, $sort_value, $reverse = false){
    $value = $result = array();
    
    foreach($array as $key => $rows){
        $value[$key] = strtolower($rows[$sort_value]);
    }
    
    if($reverse == true){
        arsort($value);
    }else{
        asort($value);
    }
    
    foreach($value as $keys => $null){
        $result[] = $array[$keys];
    }
    
    return $result;
}
?>

Examples

<?php

$array = array(array('a' => 'foo'), array('a' => 'foo4'), array('a' => 'foo2'), array('a' => 'foo3'));
print_r($array);
//Array ( [0] => Array ( [a] => foo ) [1] => Array ( [a] => foo4 ) [2] => Array ( [a] => foo2 ) [3] => Array ( [a] => foo3 ) )

print_r(sort_array($array, 'a'));
//Array ( [0] => Array ( [a] => foo ) [1] => Array ( [a] => foo2 ) [2] => Array ( [a] => foo3 ) [3] => Array ( [a] => foo4 ) )

print_r(sort_array($array, 'a', true));
//Array ( [0] => Array ( [a] => foo4 ) [1] => Array ( [a] => foo3 ) [2] => Array ( [a] => foo2 ) [3] => Array ( [a] => foo ) ) 

?>