title: how, in R, to plot time of day versus calendar date
body: <p>I regret that I come to post here after being burned-out on hours of Internet searching regarding this simplistic question.</p>
  
  <p>I have several data sets to plot in R, each consisting of two columns of data: time, date.  I am using R 2.11.0 on a Windows computer, via the Rgui.</p>
  
  <p>Time is "time of day" that an event is observed. As an example, it is recognized as:</p>
  
  <pre><code>Factor w/ 87 levels "5:53","5:54",..: 84 85 85 85 86 ...
  </code></pre>
  
  <p>Date is calendar date, recognized as:</p>
  
  <pre><code>Class 'Date'  num [1:730] 13879 13880 13881 13882 13883 ...
  </code></pre>
  
  <p>The time values are recorded in the format of a 24-hr clock, h:mm or hh:mm.  The date values are displayed yyyy-mm-dd.</p>
  
  <p>I want to plot time (y-axis) vs. date (x-axis).  </p>
  
  <p>Using </p>
  
  <pre><code>plot(date,time)
  </code></pre>
  
  <p>gives an accurate-looking plot, but the y-axis is labeled as the numeric factor values (about 0 to 90), rather than the desired, temporally-ordered levels of the factor variable.  The x-axis is labeled in the desired, human-readable format.</p>
  
  <p>How can I correct this?  Is there a "time of day" format in R that I can convert my "time" variable into?  I will subsequently like to do arithmetic on the time values as well, and would not mind having to carry one column of values to use in plotting and one column of values for maths.</p>
  
  <p>I ran across several examples online of manipulation of (date + time) variables in R, and converting those to different formats.  I do not believe this is my problem, as I have separate fields for time and date and want to plot one against the other.</p>
  
  <p>My thanks to you in advance for your suggestions, or your directions to a web-accessible resource (no appropriate libraries or bookstores at my location).</p>