title: PHP: Search multidimensional array => get array_keys
body: <p>What's the best/fastest way to get the keys of an array by a search of a value in the 2nd level arrays?</p>
  
  <pre><code>$test = array(
      'name_01' =&gt; array('yellow', 'red', 'blue', 'black', 'white', 'purple'),
      'name_02' =&gt; array('red', 'blue', 'white', 'green'),
      'name_03' =&gt; array('blue', 'pink', 'purple', 'blue'),
      'name_04' =&gt; array('white', 'black', 'red'),
      'name_05' =&gt; array('yellow', 'white', 'pink', 'black')
  );
  </code></pre>
  
  <p>For example the search by <strong>pink</strong> should return <code>array('name_03', 'name_05')</code></p>