PHP recursive issue

Hi I am trying to find the longest string in the following array:

$niza = array( array(5, 1.15 , 15),
array('unknown', 0.75 , 5, array(2, 'bla', 1.15) ),
array(array('text'), 1.15 , 7)

I am using the following function but I dont get the desired result, the value of $len remains unchanged. Can you help me?

function getLongest($array){
$longest="";
$len=0;

function arrWalk($item){
    global $len;
    global $longest;
    if(is_string($item)) {
        echo $len . "<br>";
        if (strlen($item) > $len) {
            $longest = $item;
            $len = strlen($item);
        }
    }
}

array_walk_recursive($array,'arrWalk');

echo $len;

}

arrWalk($niza);

To get longest string element from array you can use below the recursive function.

$niza = array(
    array(5, 1.15 , 15),
    array(
        'unknown', 0.75 , 5,
        array(2, 'bla', 1.15)
    ),
    array(array('text'), 1.15 , 7)
);

$longestString = '';
function getLongestString( $param )
{
    global $longestString;

    if ( is_array($param) )
    {
        foreach ($param as $val)
        {
            if ( is_string($val) && strlen($val) > strlen($longestString) )
            {
                $longestString = $val;
            }
            else
            {
                getLongestString( $val );
            }
        }
    }
    elseif ( is_string($param) && strlen($param) > strlen($longestString) )
    {
        $longestString = $param;
    }
}

getLongestString( $niza );

print $longestString;