title: Python pandas groupby aggregate on multiple columns, then pivot
body: <p>In Python, I have a pandas DataFrame similar to the following:</p>
  
  <pre><code>Item | shop1 | shop2 | shop3 | Category
  ------------------------------------
  Shoes| 45    | 50    | 53    | Clothes
  TV   | 200   | 300   | 250   | Technology
  Book | 20    | 17    | 21    | Books
  phone| 300   | 350   | 400   | Technology
  </code></pre>
  
  <p>Where shop1, shop2 and shop3 are the costs of every item in different shops.
  Now, I need to  return a DataFrame, after some data cleaning, like this one:</p>
  
  <pre><code>Category (index)| size| sum| mean | std
  ----------------------------------------
  </code></pre>
  
  <p>where size is the number of items in each Category and sum, mean and std are related to the same functions applied to the 3 shops. How can I do these operations with the split-apply-combine pattern (groupby, aggregate, apply,...) ?</p>
  
  <p>Can someone help me out? I'm going crazy with this one...thank you!</p>