title: Convert three column text file to matrix
body: <p>Hi I'd like to convert a file that's tab delimited and looks like this:</p>
  
  <pre><code>Species Date Data
  1       Dec   3 
  2       Jan   4
  2       Dec   6
  2       Dec   3
  </code></pre>
  
  <p>to a matrix like this (species is the row header):</p>
  
  <pre><code>    1  2
  Dec 3  9
  Jan    4
  </code></pre>
  
  <p>I'm guessing the part of the solution is to create a dictionary with two keys and use defaultdict to append new values to a key pair. I'd like to spit this out into tab-delimited form but also get into a format so that I can use the cluster part of scipy.</p>