title: time series plot with x axis in "year"-"month" in R
body: <p>I have a "monthly data" I want to plot the data such that I get a date in the format <code>%Y-%m" (2001-01)</code> on the x-axis.  Say my data is <code>pcp &lt;- rnorm(24)</code>. </p>
  
  <p>I have tried:  </p>
  
  <pre><code>PCP &lt;- ts(pcp, frequency = 12, start = 2001)
  plot(PCP) 
  </code></pre>
  
  <p>but the plot only has years on the x-axis.</p>
  
  <p>How do I get a plot with the date format I desire on the x-axis?</p>