[R] How to get week of the year, scale 1-52?

[Lauri Nikkinen]

R users,

I have a vector of dates

days <- seq(as.Date("2007/1/1"), as.Date("2008/1/31"), "days")

and I would like to have week numbers from 1 to 52 for each year. How
do I do that? Now I get 00-53 using

format(days, "%W")

> range(format(days, "%W"))
[1] "00" "53"

I have read "Date and Time Classes in R" (R news 01/04 by Gabor
Grothendieck and Thomas Petzoldt) with no help.

Thanks
Lauri