title: pandas calculate/show dataframe cumsum() only for positive values and other condition
body: <p>How to make this <code>cumsum()</code> calculate and show values on new column rows only when <code>df.col_2 == 'closed'</code> and <code>df.col_values &gt; 0</code> :</p>
  <p><code>df['new_col'] = df.groupby('col_1')['col_values'].cumsum()</code></p>