title: Slice groupby.describe dataframe
body: <p>I have a dataframe that looks like the following:</p>
  
  <p><a href="https://i.stack.imgur.com/eBcsp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/eBcsp.png" alt="enter image description here"></a></p>
  
  <p>I'd like to take all of the outer index, and only the mean and std from the inner index.</p>
  
  <p>I attempted to use <code>idx = pd.IndexSlice</code> in the following ways:
  <code>desc_df.loc[idx[:]]</code> yields the entire dataframe</p>
  
  <p><code>desc_df.loc[idx[3:4,:]]</code> yields only index 3 and 4</p>
  
  <p><code>desc_df.loc[idx[3:4,'mean']]</code> fails with <code>mean</code> is no in the columns</p>
  
  <p><code>desc_df.loc[idx[(3:4,'mean')]]</code> fails...etc</p>
  
  <p>How do I execute my desired use case?</p>