On Jun 29, 2010, at 7:17 PM, Jonathan Greenberg wrote:
Pardon the barrage of time series related questions, but another issue
I'm trying to solve is how to determine a sequence of dates a la
seq.dates() except going BACKWARDS in time, e.g. if seq.dates()
allowed for the to variables to be set alone, rather than the from=.
Ultimately, I'd like to have a set of dates preceding a given date in
predefined intervals (the same ones seq.dates() uses would be fine).
Thoughts? Would there be an easy way to reverse engineer a starting
date given the by= variable and the length=? With the exception
of using by=days, I'm a bit unfamiliar with how to easily determine
what date was, say, 4 months ago without doing a lot of string hacking
(seq.dates() conveniently keeps the days of the month constant when
generate date sequences, which is what I'd like).
--j
Jonathon,
Do you mean something like:
seq(as.Date(2010-07-29), length = 2, by = -4 months)
[1] 2010-07-29 2010-03-29
?
Note that the 'by' argument can be a negative interval. See the third bullet in
the Details section of ?seq.Date.
HTH,
Marc Schwartz
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