title: In Scala, how can I do the equivalent of an SQL SUM and GROUP BY?
body: <p>For example, suppose I have</p>
  
  <pre><code>val list: List[(String, Double)]
  </code></pre>
  
  <p>with values</p>
  
  <pre><code>"04-03-1985", 1.5
  "05-03-1985", 2.4
  "05-03-1985", 1.3
  </code></pre>
  
  <p>How could I produce a new List</p>
  
  <pre><code>"04-03-1985", 1.5
  "05-03-1985", 3.7
  </code></pre>