Dear all,
I wish to create a POSIXct variable from date and time variables using the
ymd_hm function in package lubridate. In some cases data for time is missing,
which causes a problem for ymd_hm. I wish to find a smooth way to handle this.
# Some example data:
x <- data.frame(date = c("2011-09-22", "2011-07-28"), time = c("15:00", NA))
x
# paste date and time together to a format that ymd_hm recognizes
x$datetime <- with(x, ifelse(!is.na(time), paste(date, time, sep = " "), NA))
x
# try ymd_hm on rows with complete data on date and time.
# install.packages("lubridate")
# library(lubridate)
ymd_hm(x$datetime[!is.na(x$time)])
#Looks OK
# try on the whole data frame:
ymd_hm(x$datetime)
# missing data causes error. Fair enough.
# try to allocate the result to the data frame on rows with complete data
x$datetime2[!is.na(x$time)] <- ymd_hm(x$datetime[!is.na(x$time)])
x
class(ymd_hm(x$datetime[!is.na(x$time)]))
class(x$datetime2)
# POSIXct is coerced to numeric. Fair enough
# try to pre-allocate a vector and convert it to class POSIXct:
x$datetime3 <- NA
class(x$datetime3) <- "POSIXct"
x
x$datetime3[!is.na(x$time)] <- ymd_hm(x$datetime[!is.na(x$time)])
x
# something happened with the time (15:00 vs 17:00). A time zone issue?
tz(x$datetime3[!is.na(x$time)])
Sys.timezone()
x$datetime3 <- with_tz(x$datetime3, "CEST")
x
# warnings, but correct time
# another 'random' try
x$datetime3 <- NA
x
class(x$datetime3) <- "POSIXct"
x$datetime3[!is.na(x$time)] <- ymd_hm(x$datetime[!is.na(x$time)])
x
tz(x$datetime3)
x$datetime3 <- with_tz(x$datetime3, "UTC")
x
# works, but I don't understand why.
#------------------------------------------
sessionInfo()
R version 2.14.2 (2012-02-29)
Platform: i386-pc-mingw32/i386 (32-bit)
locale:
[1] LC_COLLATE=Norwegian (Bokmål)_Norway.1252 LC_CTYPE=Norwegian
(Bokmål)_Norway.1252 LC_MONETARY=Norwegian (Bokmål)_Norway.1252 LC_NUMERIC=C
[5] LC_TIME=Norwegian (Bokmål)_Norway.1252
attached base packages:
[1] grDevices datasets splines graphics stats tcltk utils
methods base
other attached packages:
[1] lubridate_1.1.0 svSocket_0.9-51 TinnR_1.0.3 R2HTML_2.2
Hmisc_3.9-2 survival_2.36-12
loaded via a namespace (and not attached):
[1] cluster_1.14.2 grid_2.14.2 lattice_0.20-0 plyr_1.7.1 stringr_0.6
svMisc_0.9-63 tools_2.14.2
Windows 7
#------------------------------------------
I am sure I am missing something. Can anyone point me to a smooth way to handle
the time zones (if that is *the* problem here...)?
Thanks a lot in advance for taking your time.
Best regards,
Henrik
--
Henrik Pärn
Centre for Conservation Biology
Department of Biology
Norwegian University of Science and Technology
NO-7491 Trondheim
NORWAY
Office: +47 735 96084
Mobile: +47 909 89 255
Fax: +47 735 96100
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