On 2/1/2010 3:57 PM, Brian Diggs wrote:
> The following code:
>
> cut(as.POSIXct("2009-11-01 04:00:00", tz="America/Los_Angeles"), "1 day")
>
> gives the error:
>
> Error in seq.int(0, to - from, by) : 'to' must be finite
>
> This is related to November 1st, 2009 being the switchover date from
> daylight savings time to standard time in the America/Los_Angeles
> time zone. In particular, in cut.POSIXt, the starting time (start)
> is converted to a POSIXlt, and the individual members are
> manipulated. Because a spacing of "1 day" is requested, the hour,
> minute, and second are manually set to 0. In doing so, the
> represented time is now before the 2:00am PDT->PST change. This
> value is passed to seq.int (as the argument from), which dispatches
> to seq.POSIXt. seq.POSIXt eventually does from <-
> unclass(as.POSIXct(from)) which evaluates to NA because
> as.POSIXct(from) is NA. The seq.int call in the next line then
> passes NA as the "to" argument, causing the output error (which comes
> from the C-code of seq.int).
>
> Bringing it all together, the sequence of commands that causes the
> problems is:
>
> tm <- as.POSIXlt("2009-11-01 04:00:00", tz="America/Los_Angeles")
> tm$hour <- 0
> as.POSIXct(tm)
> # [1] NA
>
> Is there a timezone/daylight savings time safe way to get to the
> beginning of the day in cut.POSIXt so that invalid dates are not sent
> to the other functions? Alternatively, can as.POSIXct.POSIXlt be
> made to handle these manually manipulated dates correctly?
I realized I forgot my session info:
> sessionInfo()
R version 2.10.1 (2009-12-14)
i386-pc-mingw32
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
> -- Brian Diggs, Ph.D. Senior Research Associate, Department of
> Surgery, Oregon Health & Science University
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