title: Numpy Sum from a multidimensional array?
body: <p>If I had data such as: </p>
  
  <pre><code>data = [[3, 2014], [4, 2014], [6, 2013], [6,2013]] etc...
  </code></pre>
  
  <p>What is the best way to calculate the sum by year in python?  </p>