Hi Dan,
Thank you for your answer. I 'll try to provide some more information:
I have only hourly data that go from 1:00:00 to 24:00:00, no minutes or
seconds. These data represent the average of measured valuesof the previous
hour (so 1:00:00 is the average of 0:00:00 to 1:00:00 data).
I can indeed substract 1 hour from all date/time values to solve the
problem. However, I would also like to look at hourly variation within a day
and then you always need to take into account the difference of 1 hour,
which will get confusing.
So, the easiest would be to convert all 0:00 values to 24:00 and set the
date one day back.
z.dr <- data.frame(times=c(seq.POSIXt(ISOdate(2011,1,1), ISOdate(2011,1,31),
by ="hour" )))
This generates a date/time serie looking like mine but shorter. Then I tried
converting all 0:00 to 24:00 values by the following loop:
for(i in nrow(z.dr)) {
z.dr$times[i] <- ifelse(as.numeric(format(z.dr$times[i], "%H"))=="0",
z.dr$times[i]+86400, z.dr$times[i])
}
However, here I get the error "Error in as.POSIXct.numeric(value) : 'origin'
must be supplied". Without the loop it works, but the output is a numerical
value.
This is also not a good solution because the day is not changed by this
command.
Or is this just not possible to change?
Regards,
Sandy
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