title: How to plot continous data that depends on column value
body: <p><strong>What I want</strong></p>
  <p>I need to plot a graph like this with dataframe below:
  <a href="https://i.stack.imgur.com/fpqFP.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fpqFP.png" alt="enter image description here" /></a></p>
  <pre>
  
  0   Buy 2021-06-15 0:00:00  60
  1   Sale    2021-06-17 0:00:00  11
  2   Sale    2021-06-17 0:00:00  4
  3   Sale    2021-06-17 0:00:00  2
  4   Sale    2021-06-18 0:00:00  1
  5   Sale    2021-06-18 0:00:00  2
  6   Sale    2021-06-19 0:00:00  1
  7   Sale    2021-06-21 0:00:00  1
  8   Sale    2021-06-22 0:00:00  1
  9   Sale    2021-06-23 0:00:00  1
  10  Sale    2021-06-25 0:00:00  3
  11  Sale    2021-06-30 0:00:00  3
  12  Buy 2021-06-30 0:00:00  50
  13  Sale    2021-07-01 0:00:00  2
  14  Sale    2021-07-01 0:00:00  6
  15  Sale    2021-07-02 0:00:00  1
  16  Sale    2021-07-02 0:00:00  3
  17  Sale    2021-07-03 0:00:00  1
  18  Sale    2021-07-03 0:00:00  2
  </pre>
  <p>I was trying to plot with <code>cumsum()</code> but I need to first convert rows with 'Sale' to negative values in order to do that.</p>
  <p>Is there a better way to do?</p>