title: Rename result columns from Pandas aggregation ("FutureWarning: using a dict with renaming is deprecated")
body: <p>I'm trying to do some aggregations on a pandas data frame. Here is a sample code:</p>
  
  <pre><code>import pandas as pd
  
  df = pd.DataFrame({"User": ["user1", "user2", "user2", "user3", "user2", "user1"],
                    "Amount": [10.0, 5.0, 8.0, 10.5, 7.5, 8.0]})
  
  df.groupby(["User"]).agg({"Amount": {"Sum": "sum", "Count": "count"}})
  
  Out[1]: 
        Amount      
           Sum Count
  User              
  user1   18.0     2
  user2   20.5     3
  user3   10.5     1
  </code></pre>
  
  <p>Which generates the following warning:</p>
  
  <blockquote>
    <p>FutureWarning: using a dict with renaming is deprecated and will be
    removed in a future version   return super(DataFrameGroupBy,
    self).aggregate(arg, *args, **kwargs)</p>
  </blockquote>
  
  <p>How can I avoid this?</p>