title: How to merge an aggregate output back to original dataframe
body: <p>So for generalized purposes of approach:</p>
  
  <pre><code>df= [['A' , 'B']] (dataframe is actually bigger but for simplicity)
  
  SC = df[['A','B']].groupby('A').agg({'B': ['mean', 'std']})
  </code></pre>
  
  <p>I'm trying to get the output of this back into original <code>df</code> so output can be:</p>
  
  <pre><code>df=[['A','B','mean of B','std of B']]
  </code></pre>
  
  <p>I tried: <code>pd.merge(df, SC, on=None)</code>,
  got error: </p>
  
  <blockquote>
    <p>"MergeError: No common columns to perform merge on"</p>
  </blockquote>
  
  <p>Any help would be greatly appreciated, simplistically if possible.</p>
  
  <p>Thank you</p>