title: Transform table by creating columns out of row groups
body: <p>I have a table with time series data grouped by name (with some dates missing), and would like to transform the table by creating a column for each group containing that group's data. In other words, how do I go from this</p>
  
  <pre><code>x:([] name:`a`a`a`b`b`c`c;date:2000.01.01 2000.01.02 2000.01.03 2000.01.01 2000.01.02 2000.01.02 2000.01.03;val:1 2 3 1 2 3 1)
  </code></pre>
  
  <p>to this?</p>
  
  <pre><code>([] date:2000.01.01 2000.01.02 2000.01.03;a:1 2 3;b:1 2 0N;c:0N 3 1)
  </code></pre>