title: R plot with an x time axis: how to force the ticks labels to be the days?
body: <p>I have this file in csv format:</p>
  
  <pre><code>timestamp,pages
  2011-12-09T11:20:50.33,4
  2012-01-23T17:44:02.71,132
  2012-01-28T15:07:59.34,168
  </code></pre>
  
  <p>The first column is a timestamp, the second one is a page count.
  I need to plot the page count on the vertical axis and the timestamp on the horizontal axis.</p>
  
  <p>The timestamps are not regularly spaced, I have one day in december ant two close days in january.</p>
  
  <p>I tried this code</p>
  
  <pre><code>df = read.csv("my_data.csv")
  df$timestamp = strptime(df$timestamp, "%Y-%m-%dT%H:%M:%S")
  plot(df$timestamp,df$pages)
  </code></pre>
  
  <p>and I got a plot with just one tick on the middle of the x axis and with the label "Jan": it's not wrong but I would like to have three ticks with just the day number and the month.</p>
  
  <p>I tried </p>
  
  <pre><code>plot(df$timestamp,df$pages,xaxt="n")
  axis.Date(1,df$timestamp,"days")
  </code></pre>
  
  <p>but no x axis is plotted.
  Any idea?
  Thank you</p>