On Wed, 21 Jan 2009, Sergey Goriatchev wrote:
Dear Gabor,
Thanks for that!
Still, it is not really similar to how EDATE works.
With julian(Sys.Date(), Sys.Date() - 10) one moves 10 days back.
The problem is that I need to move by months, not by days, as months
have different number of days.
I need to come to the same day when I move backward or forward in
time, for example going back one month from today (21.01.2009) I need
to come to 21.12.2008.
I've read through your article in RNews 4/1 but still do not know how
to do what I need to do.
The trick is to use the POSIXlt class. E.g.
x <- Sys.Date()
xx <- as.POSIXlt(x)
xx$mon <- xx$mon - 6
as.Date(xx)
[1] "2008-07-21"
Now, the issue is what date is 6 months before 2008-08-31, and I'll
leave you to ponder what that means.
Regards,
Sergey
On Wed, Jan 21, 2009 at 10:44, Gabor Grothendieck
<ggrothendi...@gmail.com> wrote:
See ?julian
julian(Sys.Date(), Sys.Date() - 10) # 10
[1] 10
attr(,"origin")
[1] "2009-01-11"
and R News 4/1.
On Wed, Jan 21, 2009 at 4:37 AM, Sergey Goriatchev <serg...@gmail.com> wrote:
Hello, everyone
I wonder if R has something similar to Excel function
EDATE(start_date; months) which returns a serial number of the date
that is the indicated number of months before of after the start date.
Example (the second column EDATE(first_column; -6)):
01.01.1999 01.07.1998
02.02.1999 02.08.1998
06.03.1999 06.09.1998
I am working with a zoo object where the row names are dates and for
particular rows I need to find values that were recorded 6 months
before (or return NA if the date is before the timeseries start).
Maybe someone knows a passable R function for that kind of operation?
Thanks in advance for help!
Best,
Sergey
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