title: How to split time column into intervals (say 30 min or 1 h) and plot it against Date or Month
body: <p>I am trying to plot time by intervals say 15 min, 30 min or 1 hour on x-axis but I am not getting the right plot. </p>
  
  <p>My data frame is <code>transform_time</code> and it has 1000+ records. I have used:</p>
  
  <pre><code>ggplot(transform_time, aes(x = transform_time$TIME_START, y=transform_time$TIME_END, col=EVENT_TYPE)) +
     geom_line(size = 1) + 
     scale_x_datetime(limits = c(as.POSIXct("2014-05-01 00:00:00"), as.POSIXct("2014-05-31 23:59:59"))) +
     scale_x_continuous(breaks=0:31, limits=c(0,31))
  
  ggplot(Bad_Node, aes(x=transform_time$TIME_START, y=transform_time$OAR_INCIDENT_ID)) +
     geom_point()
  
  EVENT_TYPE      DATE           TIME_START    TIME_END
  event A         9/18/2014      14:47:01      16:53:07
  event B         9/18/2014      15:52:16      17:08:30
  event A         9/18/2014      16:26:19      16:53:58
  event C         9/20/2014      19:25:51      19:25:51
  event B         9/23/2014       3:40:39       4:38:07
  event D         9/25/2014       8:15:40       8:59:40
  </code></pre>
  
  <p>I want to plot time with the above mentioned intervals on X-axis. </p>