R help - May 2004 - Plotting Time against Date for time series data?

Dear all,

I have a data set containing GPS fixes of animal locations. To check that 
the GPS's are working properly, I would like to plot the time of the fixes 
(y-axis) against the date of the fixes (x-axis). If all works well, the 
plot should show four regular fixes per day. The x-axis should be labelled 
with month/year (i.e. 11/04) and the y-axis by hour from 00 to 24. I would 
like to control the x-axis limits.

I have looked at several date and time related help pages, but get horribly 
lost in all the terminology. The main challenge is to isolate date and time 
from the date/time object for plotting (marked ???). Therefore, I would 
like the following example code to work:

 >
 >
dates <- c("02/27/92", "02/27/92", "01/14/92",
"01/14/92", "03/28/92",
"03/28/92") #
times <- c("23:03:20", "10:29:56", "01:03:30",
"13:03:30", "18:21:03",
"06:56:26") #
x <- paste(dates, times) #
DateTime <- strptime(x, "%m/%d/%y %H:%M:%S") #

Date <- DateTime ??? #
Time <- DateTime ??? #
plot(x=Date, y=Time,
         xlab= "Date (month/year)", ylab= "Time (hours)",
xaxt="n", yaxt="n",
         xlim=c(as.Date("01/01/92", format="%m/%d/%y"),
as.Date("04/01/92",
format="%m/%d/%y")),
         ylim=c(0, 24)
         ) #
r <- as.POSIXct(round(range(Date), "days")) #
axis.POSIXct(1, at=seq(r[1], r[2], by="month"),
format="%m/%y") #
r <- as.POSIXct(round(range(Time), "hours")) #
axis.POSIXct(2, at=seq(r[1], r[2], by="hour"), format="%H")
#
 >
 >

Thanks for any suggestions,

Sander Oom.



--------------------------------------------------------------
Dr. Sander P. Oom
Animal, Plant and Environmental Sciences
University of the Witwatersrand
Private Bag 3
Wits 2050
South Africa

Tel (work)      +27 (0)11 717 64 04
Tel (home)      +27 (0)18 297 44 51
Fax             +27 (0)18 299 24 64

Email   sander at oomvanlieshout.net
Web     www.oomvanlieshout.net/sander

On Mon, 17 May 2004, Slist wrote:
> I have a data set containing GPS fixes of animal locations. To check that 
> the GPS's are working properly, I would like to plot the time of the
fixes
> (y-axis) against the date of the fixes (x-axis). If all works well, the 
> plot should show four regular fixes per day. The x-axis should be labelled 
> with month/year (i.e. 11/04) and the y-axis by hour from 00 to 24. I would 
> like to control the x-axis limits.
> 
> I have looked at several date and time related help pages, but get horribly
> lost in all the terminology. The main challenge is to isolate date and time
> from the date/time object for plotting (marked ???). Therefore, I would 
> like the following example code to work:
> 
>  >
>  >
> dates <- c("02/27/92", "02/27/92",
"01/14/92", "01/14/92", "03/28/92",
"03/28/92") #
> times <- c("23:03:20", "10:29:56",
"01:03:30", "13:03:30", "18:21:03",
"06:56:26") #
> x <- paste(dates, times) #
> DateTime <- strptime(x, "%m/%d/%y %H:%M:%S") #
Why do you end lines with #?  It is rather confusing.

Date <- trunc(DateTime, "day")
Time <- DateTime - Date
plot(Date, Time)

appears to do what you want (except the x axis labelling, which you can 
alter by a call to axis.POSIXct and x-axis limits, which need to be set 
via xlim as a POSIXct object.).

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595