title: How do you use pandas to find columns containing the name "add-on" and then append them to the previous column?
body: <p>The dataframe looks like this:</p>
  <pre><code>date               pencils    notebooks   notebooks add-on   bookbag   bookbag add-on   pens
  2020-01-01 5:00    12         5           3                  6         2                8
  2020-01-01 6:00    10         7           2                  9         3                14
  ...
  2020-31-01 23:55   18         4           6                  9         0                10
  </code></pre>
  <p>In pandas I want to find any column names that contains the word &quot;add-on&quot; and then sum that with the column before it. So for instance, <code>notebook add-on</code> since that contains the word add-on I need to append that to the column right before it named <code>notebooks</code>. The column <code>notebooks add-on</code> should no longer be a column name but combined/summed into the notebooks column. For example the result of the notebook column should look like:</p>
  <pre><code>   notebooks
     8
     9
     10
  </code></pre>
  <p>the same process should be true for any columns that contain the word &quot;add-on&quot;. Columns that do not contain the word &quot;add-on&quot; should stay the same.</p>
  <p>How would this be done in pandas?</p>