R help - Apr 2012 - Extracting week number starting from a specific date

Hello,

I have a list of dates, such as

dates<-
as.Date(c("1996-03-29","1996-05-30","1996-09-28","1996-05-09"))

from which I would like to extract the week number for each date, with week
n?1 being the week going from Dec 30th 1995 to Jan 6th 1996
("1995-30-12" to
"1996-06-01"). Any suggestion for a simple way to do that?

Thank you

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Hello,

Try


#
# Adapted from several posts to R-Help,
# mostly by David Winsemius, also by Gabor Grothendiek.
#
nweek <- function(x, format="%Y-%m-%d", origin){
	if(missing(origin)){
		as.integer(format(strptime(x, format=format), "%W"))
	}else{
		x <- as.Date(x, format=format)
		o <- as.Date(origin, format=format)
		w <- as.integer(format(strptime(x, format=format), "%w"))
		2 + as.integer(x - o - w) %/% 7
	}
}

dates<-
as.Date(c("1996-03-29","1996-05-30","1996-09-28","1996-05-09"))

nweek(dates)
nweek(dates, origin="1995-12-30")


Note that you have used two different date formats, Y-m-d (dates vector) and
Y-d-m (origin).
Above the origin is consistent with the rest.

Hope this helps,

Rui Barradas



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