Looking for a special date function in R
Dear Prof. Ripley, Thank you for help. Yes, that is an interesting question you pose. I already thought myself how February should be handled, as EDATE(31.08.2008; -6) returns 29.02.2008. In Excel it is not a problem, since this nonexisting date is then used in VLOOKUP function where one can have Range.Lookup argument set to TRUE and then it finds the closest value. Example from Excel (value for 29.02.2008 is recovered from the sorted table with VLOOKUP function): 21.07.2008 10.00 31.08.2008 20.00 28.02.2008 30.00 01.03.2008 40.00 02.03.2008 50.00 03.03.2008 60.00 29.02.2008 30 I wonder if that kind of functionality is available in R, or one has to write a piece of code oneself to acheive it. Thank you for your time and help! Regards, Sergey
On Wed, Jan 21, 2009 at 12:44, Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:
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 <ggrothendieck at 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 <sergeyg at 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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-- I'm not young enough to know everything. /Oscar Wilde Experience is one thing you can't get for nothing. /Oscar Wilde When you are finished changing, you're finished. /Benjamin Franklin Tell me and I forget, teach me and I remember, involve me and I learn. /Benjamin Franklin Luck is where preparation meets opportunity. /George Patten
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
-- Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595
I'm not young enough to know everything. /Oscar Wilde Experience is one thing you can't get for nothing. /Oscar Wilde When you are finished changing, you're finished. /Benjamin Franklin Tell me and I forget, teach me and I remember, involve me and I learn. /Benjamin Franklin Luck is where preparation meets opportunity. /George Patten