[R] Time differences (as.difftime?) issue

From: Lukas Rode <lukas.rode_at_googlemail.com>
Date: Wed, 14 May 2008 17:12:32 +0200


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"

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

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"

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