title: How to provide a groupby of dates with a count from a categorical column separately
body: <p>I have a transactional table that lists the gender of each person who started in one column, and the date they started in another. I want to perform a groupby that results in a data frame with a count of each gender by date. Any idea?</p>
  <pre><code>    Gender  LastStart
  1   M   2013-05-21
  2   M   2013-05-24
  3   F   2013-05-27
  4   M   2013-05-27
  5   F   2013-05-28
  6   F   2013-05-28
  </code></pre>
  <p>Should result in</p>
  <pre><code>             M   F
  2013-05-21   1   0
  2013-05-24   1   0
  2013-05-27   1   1
  2013-05-28   0   2
  </code></pre>
  <p>I think I need to run a groupby over a list and then a pivot but my groupby is producing a series so the pivot won't work. I'm very confused so any help much appreciated!</p>