I have a data frame with variable "datetime" which is of class POSIXct.
Consecutive observations are separated by 30 minutes.
However, some of the differences reported by R give unexpected results.
For example consider the following two consecutive entries:
> par.dat$datetime[5944]
[1] "2010-04-04 02:30:00 EST"
> par.dat$datetime[5945]
[1] "2010-04-04 03:00:00 EST"
When I examine the difference, R reports 1.5 hours instead of 30 minutes:
> par.dat$datetime[5945]-par.dat$datetime[5944]
Time difference of 1.5 hours
On further investigation it appears there's something peculiar to this
particular date. Other years work fine, eg:
> as.POSIXct("2011-04-04 03:00:00")- as.POSIXct("2011-04-04 02:30:00")
Time difference of 30 mins
> as.POSIXct("2012-04-04 03:00:00")- as.POSIXct("2012-04-04 02:30:00")
Time difference of 30 mins
> as.POSIXct("2009-04-04 03:00:00")- as.POSIXct("2009-04-04 02:30:00")
Time difference of 30 mins
But when I use 2010 I get a difference of 1.5 hours:
> as.POSIXct("2010-04-04 03:00:00")- as.POSIXct("2010-04-04 02:30:00")
Time difference of 1.5 hours
Any suggestions?
Thanks,
David Fox.
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