title: How to set dates in x axis with non-uniform interval?
body: <p>I would like to draw a time-plot using the <code>matplotlib.dates</code> module. From the tutorial, I know how to set regular interval date like the following:</p>
  
  <pre><code>ax.xaxis.set_major_locator(DayLocator())
  ax.xaxis.set_major_formatter(DateFormatter("%Y-%m"))
  ax.xaxis.set_minor_...
  </code></pre>
  
  <p>However, in my data there are some months missing. My xaxis date is more like : Jan, Feb, May, Jul, Sep, Oct, Sep... no pattern is formed...</p>
  
  <p>How can I deal with such situation?.</p>