array_search doesn't work on a nested array : <pre><code>$needle = 'foo';

$haystack = [
    'bar' =&gt; [ 'foo' ],
    'baz' =&gt; [ 'qux' ]
];

// if 'foo' in of the arrays of $haystack, return its key
// in this case its 'bar'
</code></pre>

<p><code>array_search</code> seems to work on simple arrays. What do I need for my case?</p>
