title: How do you remove first row of each groupby aggregate dataframe?
body: <p>I currently have this function:</p>
  <pre><code>def process_data(data):
      data = data[data['Bucket Number'] == 25.0].groupby(['Activity Month', 'Agent Sign']).agg({'Total Ping Current Forecast': [np.sum]})
      data = data.sort_values(['Activity Month', ('Total Ping Current Forecast', 'sum')], ascending=[True, False]).groupby(level=0).head(3)
      return data
  </code></pre>
  <p>Which produces this output:</p>
  <pre><code>                          Total Ping Current Forecast
                                                    sum
  Activity Month Agent Sign                            
  202001         {Various}                 1.305513e+09
                 HDQGR1                    2.171435e+08
                 CRCTLD                    4.774614e+07
  202002         {Various}                 1.159181e+09
                 HDQGR1                    1.912536e+08
                 CRCTLD                    4.573402e+07
  202003         {Various}                 1.090292e+09
                 HDQGR1                    1.852591e+08
                 CRCTLD                    4.045673e+07
  </code></pre>
  <p><strong>I want to remove the first row of each group so that the output looks like this:</strong></p>
  <pre><code>                          Total Ping Current Forecast
                                                    sum
  Activity Month Agent Sign                            
  202001         HDQGR1                    2.171435e+08
                 CRCTLD                    4.774614e+07
                 DFW1DF                    1.622023e+07
  202002         HDQGR1                    1.912536e+08
                 CRCTLD                    4.573402e+07
                 HDQ1ZB                    2.711470e+07
  202003         HDQGR1                    1.852591e+08
                 CRCTLD                    4.045673e+07
                 HDQ1ZB                    1.532134e+07
  </code></pre>
  <p>Essentially, I want the highest value of each group dropped since the dataframe is already sorted in descending order by <code>sum</code>.</p>
  <p>I found <a href="https://stackoverflow.com/questions/50486098/how-to-delete-the-first-line-of-each-group-in-pandas">this solution</a> and tried this:</p>
  <pre><code>def process_data(data):
      data = data[data['Bucket Number'] == 25.0].groupby(['Activity Month', 'Agent Sign']).agg({'Total Ping Current Forecast': [np.sum]})
      data = data.sort_values(['Activity Month', ('Total Ping Current Forecast', 'sum')], ascending=[True, False]).apply(lambda x: x.iloc[1:]).groupby(level=0).head(3)
      return data
  </code></pre>
  <p>But it only applied the function to the first group giving this result:</p>
  <pre><code>                          Total Ping Current Forecast
                                                    sum
  Activity Month Agent Sign                            
  202001         HDQGR1                    2.171435e+08
                 CRCTLD                    4.774614e+07
                 DFW1DF                    1.622023e+07
  202002         {Various}                 1.159181e+09
                 HDQGR1                    1.912536e+08
                 CRCTLD                    4.573402e+07
  202003         {Various}                 1.090292e+09
                 HDQGR1                    1.852591e+08
                 CRCTLD                    4.045673e+07
  </code></pre>
  <p><strong>How do I apply that function to each group in the dataframe?</strong></p>