title: Python Pandas - Iterating inside Groupby to find time differences
body: <p>I have a <strong>Pandas dataframe</strong> which look <a href="http://i.stack.imgur.com/dWWI1.png" rel="nofollow">like this</a></p>
  
  <p>The customer number is unique to each customer, but repeats itself if the customer visits again.
  I want to groupby customer number. Then in each groupby object, I want to find out the duration between visits.</p>
  
  <p>So, I do it like this..</p>
  
  <pre><code>df['Date'] =  pd.to_datetime(df['Date'], format='%d %b %y')
  grouped = df.groupby('Customer no')
  </code></pre>
  
  <p>My question is,
  how do I iterate over the grouped rows and find out the time (in days) between subsequent visits.</p>