title: Dropping rows with NaN values on two columns
body: <p>not sure what I am missing. I am trying to drop the all rows with NaN/empty values on one of the columns. Thanks.</p>
  <pre class="lang-py prettyprint-override"><code>df.dropna(how='all', subset=['column_one', 'column_two'], axis=0, inplace=True)
  </code></pre>