title: pandas aggregate function with multiple output columns
body: <p>I am trying to define an aggregation function with more than one OUTPUT columns, which i would like to use as follows</p>
  
  <pre><code>df.groupby(by=...).agg(my_aggregation_function_with_multiple_columns)
  </code></pre>
  
  <p>any idea how to do it ?</p>
  
  <p>i tried things like</p>
  
  <pre><code>def my_aggregation_function_with_multiple_columns(slice_values):
      return {'col_1': -1,'col_2': 1}
  </code></pre>
  
  <p>but this will logically output the dictionary {'col_1': -1,'col_2': 1} in a single column...</p>