On Wed, 14 May 2008, Lukas Rode wrote:
Dear all,
I have a vector generated using the function strptime:
my.dt
[1] "2004-04-19 08:35:00 W. Europe Daylight Time" "2004-04-19 09:35:00 W.
Europe Daylight Time" "2004-04-19 11:35:00 W. Europe Daylight Time"
[4] "2004-04-19 13:35:00 W. Europe Daylight Time" "2004-04-20 07:50:00 W.
Europe Daylight Time"
class(my.dt)
[1] "POSIXt" "POSIXct"
Somehow you didn't as that is not the class of a result from strptime.
Now I would like to test if the difference from the times to the first time
is lower than a given threshold:
my.dt - my.dt[1] < threshold
The issue is, I would like to specificy the threshold as flexibly as
possible, and I tried to do this using as.difftime
as.difftime(23, '%H')
Time difference of 23 hours
However, I cannot specify a threshold larger than 23 hours in units of
hours:
as.difftime(24, '%H')
Time difference of NA secs
It's much simpler to use
as.difftime(47, units="hours")
Time difference of 47 hours
I can hack around this in the following way:
threshold <- as.difftime(23, '%H')
threshold
Time difference of 23 hours
threshold[[1]] <- 47
threshold
Time difference of 47 hours
In that way I can use my original statement:
my.dt - my.dt[1] < threshold
[1] TRUE TRUE TRUE TRUE TRUE
In summary, my question is: Is there a more elegant way than my hack from
above to specify time difference thresholds of for example 47 hours, or of
246 seconds, or of 33 days and 5 hours? This could be using as.difftime or
using other means.
Thanks in advance,
Lukas
P.S.
sessionInfo()
R version 2.4.1 (2006-12-18)
i386-pc-mingw32
locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
attached base packages:
[1] "stats" "graphics" "grDevices" "utils" "datasets" "methods"
"base"
other attached packages:
chron odfWeave XML gplots gdata
gtools RColorBrewer lattice foreign nlme
"2.3-9" "0.7.3" "1.4-0" "2.3.2" "2.3.1"
"2.3.0" "0.2-3" "0.14-16" "0.8-18" "3.1-79"
--
Brian D. Ripley, [EMAIL PROTECTED]
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
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