title: r plotting number of sales per month
body: <p>I have a dataframe that looks like this.
  The date column represents the sales date.</p>
  
  <pre><code>Date          Gender
  2015-01-01    Male
  2015-02-01    Male
  2015-02-01    Female
  2015-03-01    Male
  2015-03-01    Male
  2015-03-01    Female
  </code></pre>
  
  <p>I would like to create a graph that plots the month along the x axis.
  The two columns for male and female in different colours per month then have the number of sales along the y axis.</p>