title: How to transform Pandas df for stacked bargraph
body: <p>I have the following df resulting from:</p>
  <pre><code>plt_df = df.groupby(['Aufnahme_periode','Preisgruppe','Land']).count()
  
  
  INDEX  Aufnahme_periode  Preisgruppe Land  Anzahl
  1344       2021-11-01            1   NL       2
  1345       2021-12-01            1   AT       8
  1346       2021-12-01            1   BE       1
  1347       2021-12-01            1   CH       1
  1348       2021-12-01            1   DE     154
  1349       2021-12-01            1   GB       3
  1350       2021-12-01            1   JP       1
  1351       2021-12-01            1   NL       2
  1352       2022-01-01            1   AT       1
  1353       2022-01-01            1   DE      19
  1354       2022-01-01            1   IT       1
  1355       2022-01-01            2   CH       1
  1356       2022-01-01            2   DE       1
  1357       2022-02-01            1   DE      16
  1358       2022-02-01            1   FR       1
  1359       2022-02-01            2   CH       1
  1360       2022-03-01            1   DE      23
  </code></pre>
  <p>I would like to make two bar charts:</p>
  <p>1:</p>
  <p>Monthly signup by &quot;Preisgruppe&quot; so stack group 2 on top of group 1:</p>
  <p>The df should probably have columns for group 1 and 2 and rows for each month.</p>
  <p>2:
  Monthly signup by country:</p>
  <p>Same as above, one column for each country and rows for the months.</p>
  <p>I think I know how to make the charts, I just need help transforming the df.</p>