Count the number of times each unique leaf node value occurs in a multidimensional array

I have been trying to count the leaf node elements in a array. I'm thinking along the lines of:

• Getting a simple array of leaf elements from the input array using: array_walk_recursive().
• Count elements in the new array using: array_count_values().

I'm unsure how to get a simple list array from array_walk_recursive(), I just get a long string of values. Or is there a better way of achieving this result?

DESIRED RESULT:

flammable = 1
irritant = 2 
toxic = 3

PHP:

$testArray = [
    [
        0 => 'toxic',
        1 => 'irritant',
        3 => 'flammable',
    ],
    [
        0 => 'toxic',
        1 => 'irritant',
    ],
    [
        0 => 'toxic',
    ]
];

array_walk_recursive($testArray, function(&$value) 
{
    echo 'string = '.$value;
    print_r(newArray);              //How can i get this new array list?
});
 
$counts = array_count_values($newArray); //and use this to count values?

Try this, the numbers should show up in the $groups array.

$groups = array();

array_walk_recursive($testArray, function(&$value) use (&$groups)
{
    if (isset($groups[$value])) {
        $groups[$value]++;
    } else {
        $groups[$value] = 1;
    }
});

print_r($groups);