title: Get key of multidimensional array?
body: <p>For example, I have multidimensional array as below:</p>
  
  <pre><code>$array = array (
    0 =&gt; 
      array (
        'id' =&gt; '9',
        'gallery_id' =&gt; '2',
        'picture' =&gt; '56475832.jpg'
      ),
    1 =&gt; 
      array (
        'id' =&gt; '8',
        'gallery_id' =&gt; '2',
        'picture' =&gt; '20083622.jpg'
      ),
    2 =&gt; 
      array (
        'id' =&gt; '7',
        'gallery_id' =&gt; '2',
        'picture' =&gt; '89001465.jpg'
      ),
    3 =&gt; 
      array (
        'id' =&gt; '6',
        'gallery_id' =&gt; '2',
        'picture' =&gt; '47360232.jpg'
      ),
    4 =&gt; 
      array (
        'id' =&gt; '5',
        'gallery_id' =&gt; '2',
        'picture' =&gt; '4876713.jpg'
      ),
    5 =&gt; 
      array (
        'id' =&gt; '4',
        'gallery_id' =&gt; '2',
        'picture' =&gt; '5447392.jpg'
      ),
    6 =&gt; 
      array (
        'id' =&gt; '3',
        'gallery_id' =&gt; '2',
        'picture' =&gt; '95117187.jpg'
      )
  );
  </code></pre>
  
  <p>How can I get key of <code>array(0,1,2,3,4,5,6)</code>?</p>
  
  <p>I have tried a lot of examples, but nothing has worked for me.</p>