[R] identifying weeks (dates) that certain days (dates) fall into

[Gabor Grothendieck]

On Tue, Aug 2, 2011 at 10:36 AM, Dimitri Liakhovitski
<dimitri.liakhovitski at gmail.com> wrote:
> Hello!
>
> I have dates for the beginning of each week, e.g.:
> weekly<-data.frame(week=seq(as.Date("2010-04-01"),
> as.Date("2011-12-26"),by="week"))
> week  # each week starts on a Monday
>
> I also have a vector of dates I am interested in, e.g.:
> july4<-as.Date(c("2010-07-04","2011-07-04"))
>
> I would like to flag the weeks in my weekly$week that contain those 2
> individual dates.
> I can only think of a very clumsy way of doing it:
>
> myrows<-c(which(weekly$week==weekly$week[weekly$week>july4[1]][1]-7),
>        which(weekly$week==weekly$week[weekly$week>july4[2]][1]-7))
> weekly$flag<-0
> weekly$flag[myrows]<-1
>
> It's clumsy - because actually, my vector of dates of interest (july4
> above) is much longer.
> Is there maybe a more elegant way of doing it?
> Thank you!

This gives myrows:

   as.numeric(july4 - weekly[1,1]) %/% 7 + 1

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