title: Pandas - return a dataframe after groupby
body: <p>I have a Pandas <code>df</code>:</p>
  
  <pre><code>Name    No
  A       1
  A       2
  B       2
  B       2
  B       3
  </code></pre>
  
  <p>I want to group by column <code>Name</code>, sum column <code>No</code> and then return a 2-column dataframe like this:</p>
  
  <pre><code>Name    No
  A       3
  B       7
  </code></pre>
  
  <p>I tried:</p>
  
  <pre><code>df.groupby(['Name'])['No'].sum()
  </code></pre>
  
  <p>but it does not return my desire dataframe. I can't add the result to a dataframe as a column.</p>
  
  <p>Really appreciate any help</p>