title: Argument 2 passed to array_sort() must be callable, string given
body: <p>I have the following arrays:</p>
  
  <pre><code>  array (size=3)
      0 =&gt; 
        array (size=3)
          'id' =&gt; int 18
          'class' =&gt; string 'VIP' (length=3)
          'fee' =&gt; float 20
      1 =&gt; 
        array (size=3)
          'id' =&gt; int 19
          'class' =&gt; string 'VVIP' (length=4)
          'fee' =&gt; float 50
      2 =&gt; 
        array (size=3)
          'id' =&gt; int 20
          'class' =&gt; string 'STANDARD' (length=8)
          'fee' =&gt; float 5
  
    array (size=3)
      0 =&gt; 
        array (size=3)
          'id' =&gt; int 19
          'class' =&gt; string 'VVIP' (length=4)
          'fee' =&gt; int 50
      1 =&gt; 
        array (size=3)
          'id' =&gt; int 18
          'class' =&gt; string 'VIP' (length=3)
          'fee' =&gt; int 20
      2 =&gt; 
        array (size=3)
          'id' =&gt; int 20
          'class' =&gt; string 'STANDARD' (length=8)
          'fee' =&gt; int 5
  </code></pre>
  
  <p>Now i am trying to sort them both using <code>array_sort</code> in <strong>ascending order</strong> using the <code>id</code>.:</p>
  
  <pre><code>$array_1 = array_sort($array_1, 'id', SORT_ASC);
  $array_2 = array_sort($array_2, 'id', SORT_ASC);
  </code></pre>
  
  <p>However i keep getting the following error:</p>
  
  <blockquote>
    <p>Argument 2 passed to array_sort() must be callable, string given</p>
  </blockquote>