title: Concatenate cells with duplicate rows
body: <p>I'm trying to concatenate the information (separated by commas) of rows based on a single column duplicate value, and remove all the rest of the duplicates based on that column.</p>
  <p><strong>What I have:</strong></p>
  <pre><code>​[in]
  
  pipeline = {'Name':['Josh','Angel','Karina','Josh','Peter','Karina','Karina'],
             'Quote':['9001','9002','9003','9004','9005','9006','9007']}
  ​
  df = pd.DataFrame(pipeline)
  
  [out]​
  
  Name    Quote
  0   Josh    9001
  1   Angel   9002
  2   Karina  9003
  3   Josh    9004
  4   Peter   9005
  5   Karina  9006
  6   Karina  9007
  
  </code></pre>
  <p><strong>What I want:</strong></p>
  <pre><code>Name    Quote
  0   Josh    9001, 9004
  1   Angel   9002
  2   Karina  9003, 9006, 9007
  4   Peter   9005
  </code></pre>