title: Plotting timeseries in ggplot2
body: <p>I am working with a time series.  The first 20 rows of my real data is shown below.  I wish to:</p>
  
  <p>a. Subset my ggplot graph to a particular timeframe (e.g. only showing values between 07:46:40 and 07:49:00).</p>
  
  <p>b. I also wish to change the frquency of tick marks on the x axis. Using the example detailed bwlow I want just the whole minutes to be dispalyed on the axis (however for my proper graph, I would wish just hourly values to be displayed).</p>
  
  <p>Any advice on the above would be gratefully received.</p>
  
  <pre><code>day3 &lt;- structure(list(Date = c("11/12/2012", "11/12/2012", "11/12/2012", 
                              "11/12/2012", "11/12/2012", "11/12/2012", "11/12/2012", "11/12/2012", 
                              "11/12/2012", "11/12/2012", "11/12/2012", "11/12/2012", "11/12/2012", 
                              "11/12/2012", "11/12/2012", "11/12/2012", "11/12/2012", "11/12/2012", 
                              "11/12/2012", "11/12/2012"), Time = c("07:46:10", "07:46:20", 
                                                                    "07:46:30", "07:46:40", "07:46:50", "07:47:00", "07:47:10", "07:47:20", 
                                                                    "07:47:30", "07:47:40", "07:47:50", "07:48:00", "07:48:10", "07:48:20", 
                                                                    "07:48:30", "07:48:40", "07:48:50", "07:49:00", "07:49:10", "07:49:20"
                              ), Axis1 = c(59L, 651L, 59L, 0L, 22L, 50L, 0L, 0L, 114L, 899L, 
                                           129L, 33L, 21L, 9L, 224L, 135L, 266L, 16L, 59L, 126L), Steps = c(1L, 
                                                                                                            2L, 1L, 0L, 2L, 1L, 0L, 0L, 5L, 15L, 6L, 2L, 2L, 0L, 8L, 5L, 
                                                                                                            16L, 1L, 3L, 8L)), .Names = c("Date", "Time", "Axis1", "Steps"
                                                                                                            ), row.names = 52838:52857, class = "data.frame")
  #Creates a new dataframe with a time column.
  day3 &lt;- within(day3,{
    posb &lt;- as.POSIXlt(Time,format="%H:%M:%S")
    posb &lt;- NULL  # cleanup
  })
  
  library(ggplot2)
  g = ggplot(day3, aes(x=strptime(Time, "%H:%M:%S"), y=Axis1)) + geom_line(aes(group = 1)) +
    theme_bw() +
    xlab("Time") + 
    ylab("Activity (Counts per 10 seconds)") + 
    scale_x_datetime(limits=c(as.POSIXct("07:47:50"),as.POSIXct("07:49:10")))
  
  
  g
  </code></pre>
  
  <p><strong>Edit</strong></p>
  
  <p>if I wanted to add a text box onto my graph, how do I work with the time column?
  So far I have got:</p>
  
  <pre><code>geom_text(aes(05:00,0),label="Sedentary")
  </code></pre>
  
  <p>... but this doesn't want to work at the moment.</p>