title: Sorting an array related to another array
body: <p>I have two arrays, <code>x</code> and <code>y</code>, where y is the value of the tens of every element in <code>x</code>. Now, I want to sort <code>y</code>. But, the order of <code>y</code> will be different of <code>x</code>'s. So, I can't tell after sorting which element in <code>y</code> was related to, for instance, <code>x[0]</code>.</p>
  
  <p>I want a "double sorting" maybe.</p>