title: module 'pandas' has no attribute 'rolling_apply'
body: <p>I am using pandas with version 0.23.4 and the below code is giving me the error - "module 'pandas' has no attribute 'rolling_apply'"</p>
  
  <p>Below is the function call:</p>
  
  <pre><code>df['perLow'] = pd.rolling_apply(df.low, 2, add_percentage_diff)
  </code></pre>
  
  <p>Any help with fixing this error is much appreciated. </p>