I've just uncovered an infelicity in as.difftime:
> as.difftime(diff(as.POSIXct(c('2012-12-12', '2012-12-13'))),
units='hours')
Time difference of 1 days
Is this a bug in the code or in my understanding?
Thanks again for all your hard work in making R the great product it
is and in answering so many questions.
Best Wishes,
Spencer
> sessionInfo()
R version 2.14.1 (2011-12-22)
Platform: i386-pc-mingw32/i386 (32-bit)
locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] zoo_1.7-7 RODBC_1.3-4 WriteXLS_2.1.0 sos_1.3-1
brew_1.0-6
loaded via a namespace (and not attached):
[1] grid_2.14.1 lattice_0.20-0 tools_2.14.1
############################
I just encountered another RTFM problem: With
diff(as.POSIXct(...), ...) I was unable to control the units of the
results. Examples:
(d.d <- diff(as.POSIXct(c('2012-12-12', '2012-12-13'))))
Time difference of 1 days
(d.h <- diff(as.POSIXct(c('2012-12-12 08:00', '2012-12-12 09:00'))))
Time difference of 1 hours
(d.m <- diff(as.POSIXct(c('2012-12-12 08:00', '2012-12-12 08:01'))))
Time difference of 1 mins
(d.s <- diff(as.POSIXct(c('2012-12-12 08:00:00', '2012-12-12
08:00:01'))))
Time difference of 1 secs
as.numeric(d.d)
[1] 1
as.numeric(d.s)
[1] 1
methods('diff') identified the following:
[1] diff.Date diff.default diff.POSIXt diff.ts diff.zoo*
In looking at the help pages for each of these functions, I found
no mention of "difftime" or any other way to control the units.
methods('-')
[1] -.Date -.POSIXt -.yearmon* -.yearqtr*
?"-.Date" didn't seem helpful on this, either. ?"-.POSIXt"
contained a link to "difftime", but I didn't see that until after I read
the code for "-.POSIXt" and found "difftime".
I humbly beseech ye to consider adding a difftime example to all
these help pages.
Thanks,
Spencer
p.s. In case there is any doubt, I very much appreciate all the work
that the R Core team has invested in making R what it is today.
--
Spencer Graves, PE, PhD
President and Chief Technology Officer
Structure Inspection and Monitoring, Inc.
751 Emerson Ct.
San José, CA 95126
ph: 408-655-4567
web: www.structuremonitoring.com
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