title: GROUP BY/SUM from shell
body: <p>I have a large file containing data like this:</p>
  
  <pre><code>a 23
  b 8
  a 22
  b 1
  </code></pre>
  
  <p>I want to be able to get this:</p>
  
  <pre><code>a 45
  b 9
  </code></pre>
  
  <p>I can first sort this file and then do it in Python by scanning the file once. What is a good direct command-line way of doing this?</p>