title: How to calculate % change based on varying years and column_name
body: <p>I have a dataframe like the one below</p>
  
  <pre><code>Index     Toronto_2000   Toronto_2001    Toronto_2002    Toronto_2003    Montreal_2000  Montreal_2001   Montreal_2002   Montreal_2003
  ID:1012          100            98              102             105             101             104             108            110
  </code></pre>
  
  <p>How can I calculate the % change for each of the years and separate for each city?</p>
  
  <ul>
  <li>Like calculate df.pct_change() for 2001, 2002, 2003 given that there are different cities </li>
  </ul>