title: Find the increase, decrease in a column of pandas Dataframe
body: <p>I have a dataframe and I want to check whether the elements in the column <code>"GDP"</code> increase or decrease in comparison to their previous value to create column <code>"change"</code>. </p>
  
  <pre class="lang-none prettyprint-override"><code>Quarter:  GDP:      change
  1999q3    1934.5    ------
  1999q4    1932.3    decline
  2000q1    1930.3    decline
  2000q2    1960.7    increase
  2000q3    1989.5    increase
  2000q4    2021.9    increase
  2001q1    1771.8    decline
  2001q2    1490.3    decline
  2001q3    2035.3    increase
  </code></pre>
  
  <p>I've already tried <code>diff()</code> function but not sure how it could help. </p>