On Dec 17, 2010, at 11:08 AM, Luca Meyer wrote:
x= factor(c("2009-03-30 00:00:00", "2009-04-06 00:00:00", "2009-04-13
00:00:00", "2009-04-20 00:00:00", "2009-04-27 00:00:00", "2009-05-04
00:00:00" ,"2009-05-11 00:00:00", "2009-05-18 00:00:00"))
require(lubridate)
xd=as.POSIXct(x)
week(xd)
# [1] 13 14 15 16 17 18 19 20
year(xd)
# [1] 2009 2009 2009 2009 2009 2009 2009 2009
paste(year(xd), " W",week(xd), sep="")
#[1] "2009 W13" "2009 W14" "2009 W15" "2009 W16" "2009 W17" "2009 W18"
"2009 W19" "2009 W20"
David Winsemius, MD
West Hartford, CT
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