title: Converging Pandas Dataframe so that a column only has one value but its other column values are summed up
body: <p>I have a Pandas Dataframe as so:</p>
  
  <pre><code>fruits = ['apple', 'apple', 'banana', 'banana', 'orange']
  quantities = [10, 5, 20, 12, 25]
  products = pd.DataFrame({'Fruits': fruits, 'Amount': quantities})
  </code></pre>
  
  <p>What I want to do is converge the <code>'Fruits'</code> column so that the only entries are </p>
  
  <pre><code>'apple', 'banana', and 'orange'
  </code></pre>
  
  <p>but their 'quantities' are added up, i.e. </p>
  
  <pre><code>'apple'=15, 'banana'=32, and 'orange'=25. 
  </code></pre>
  
  <p>This would be the new dataframe.</p>
  
  <p>Any ideas?</p>