title: Remove all keys from an associative array in order to get a simple no key all-value array
body: <p>Here is the sort of array I have for instance:</p>
  
  <pre><code>Array ( 
          [0] =&gt; Array ( [id] =&gt; 21 )
          [1] =&gt; Array ( [id] =&gt; 24 ) 
        ) 
  </code></pre>
  
  <p>and I simply want to have</p>
  
  <pre><code>Array(21,24)
  </code></pre>
  
  <p>How can I do it ?</p>