[R] Date Math
pgilbert902 at gmail.com
Mon Oct 15 15:17:36 CEST 2012
On 12-10-15 06:00 AM, r-help-request at r-project.org wrote:
> My understanding is that the lag command will lag an entire time series. That isn't what I'm looking for.
> I just want, for example, today, and 5 entries back.
> for exmple:
> iter <- '2011-05-18'
> observations[iter] # works fine, returns the row at that date.
> index(observations[iter[) # just returns the iter back
> index(observations[iter]) - 5 # returns "2011-05-17 23:59:57 PDT", so it subtracted 3 seconds.
> really, I want to find: iter- 5 days.
Switching between 5 entries back and 5 days back has me confused about
whether you have more than one entry some days or not. If you mean you
have at most one entry per day, and you want the last five days that you
have observations, then this part of your problem can be solved by
switching from POSIXct to dates:
> z <- Sys.time()
 "2012-10-15 08:34:58 EDT"
> z -5
 "2012-10-15 08:34:53 EDT"
> as.Date(z) -5
(BTW, a complete example is always useful when asking for help. I think
your "obviously fails" code would be pretty close to working, depending
on how the dates were generated.)
> Noah Silverman
> Smart Media Corp.
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