Doing away with “unknown timezone” warnings

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Timezone stuff can really drive you NUTS

– at least if you’re sitting in front of a German Windows-Box ;-)

This is what I used to do to set my tz:

options(tz="Europe/Berlin")

And I always wondered why R would throw “unknown timezone” warnings:

> t <- "2011-11-08 09:42:00"
 > as.POSIXct(t, tz=getOption("tz"))
 [1] "2011-11-08 09:42:00 CET"
 Warning messages:
 1: In strptime(xx, f <- "%Y-%m-%d %H:%M:%OS", tz = tz) :
 unknown timezone 'MET-1MST'
 2: In as.POSIXct.POSIXlt(x) : unknown timezone 'MET-1MST'
 3: In strptime(x, f, tz = tz) : unknown timezone 'MET-1MST'
 4: In as.POSIXct.POSIXlt(as.POSIXlt(x, tz, ...), tz, ...) :
 unknown timezone 'MET-1MST'
 5: In as.POSIXlt.POSIXct(x, tz) : unknown timezone 'MET-1MST'

Someday I found out that setting tz via `options()` was not enough as the environment variable `TZ` is not affected and hence all the the trouble:

> Sys.getenv("TZ")
 [1] "MET-1MST"

Changing this should do away with the nasty warnings:

> Sys.setenv(TZ="Europe/Berlin")
 > Sys.getenv("TZ")
 [1] "Europe/Berlin"
 > as.POSIXct(t, tz=getOption("tz"))
 [1] "2011-11-08 09:42:00 CET"

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