Re: Dates and Times in S-Plus

[David L Lorenz <lorenz@usgs.gov>]

Kim,
  There are a lot of thing to consider
when making plots of date/time data, including getting ticks in the correct
place and correct labels. We are trying to develop functions that will
plot the data correctly and get nice ticks and correct labels. I don't
have anything for hourly data right now, but when we do get a good product,
those functions will be publically available.  Here's basically the
approach I would take:

1. For the GUI and command, I'd generate
a data.frame that contains the ticks and labels I wanted. Use the timeSeq()
function to generate ticks:
> timeSeq("11/29/2007 14:15:00",
by='hours', length.out=6, align.by=T, extend=T)
[1] 11/29/2007 14:00:00.000 11/29/2007
15:00:00.000 11/29/2007 16:00:00.000
[4] 11/29/2007 17:00:00.000 11/29/2007
18:00:00.000 11/29/2007 19:00:00.000
Use the hms() function on those data
to extract the hour and put that into another column for the labels. You
can further format them any way you wish.

2. For the GUI plot, set the major ticks
to use a column in a separate data set and choose the one you created in
step one. Do the same for labels.

3. To subset the data, use something
like:
DateTime >= timeDate("11/29/2007
14:15:00") & DateTime
<= timeDate("11/29/2007 18:15:00")
in your subsetting _expression_, assuming
that the date/time column name is DateTime.

4. For the command line version, I'd
convert everything to double for the date/time axis, set the axis type
to 'i' or 's' and not draw anything on that axis. Then go back and draw
the axis, put in the ticks and labels.

  Good luck.
Dave

Kim Elmore <Kim.Elmore@noaa.gov>
Sent by: s-news-owner@lists.biostat.wustl.edu

04/06/2007 11:16 AM

To	S-News <s-news@wubios.wustl.edu>
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Subject	[S] Dates and Times in S-Plus

I've never much worked with dates and times, but find
that I must now do 
so. I'm doing some very basic EDA and using the GUI to generate some 
plots. When making plots using the GUI, how do I control the span of the
date axis? I'm aware that S-Plus encodes the date in a manner similar to
unix/linux, but I don't know how to define things like tic marks in 
terms of, say hours. For example, if I want a tic mark every hour, how
do I declare that? Using command line plots, how would I subset the data
such that I plotted only data between, say, 11/29/2007 14:15:00 and 
11/29/2007 18:15:00?

All data are currently in a data.frame and the data type for the dates
column is timeDate.

I'm using S-Plus 7.0.6 under Windows XP.

Kim Elmore
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