That will only work if your starting date happens to be the first day of the year:
x <- seq(as.Date("2001/1/1"), as.Date("2010/1/1"), "3 months") > head(x) [1] "2001-01-01" "2001-04-01" "2001-07-01" "2001-10-01" "2002-01-01" [6] "2002-04-01" Compare that to: x2 <- seq(as.Date("2001/2/3"), as.Date("2010/1/1"), "3 months") > head(x2, 10) [1] "2001-02-03" "2001-05-03" "2001-08-03" "2001-11-03" "2002-02-03" [6] "2002-05-03" "2002-08-03" "2002-11-03" "2003-02-03" "2003-05-03" The "3 months" is literally 3 months from the defined start date, not 3 months from the first of the year. So you are not going to get calendar quarter starting dates in that case. On the other hand: > cut(x2, breaks = "quarter") [1] 2001-01-01 2001-04-01 2001-07-01 2001-10-01 2002-01-01 2002-04-01 [7] 2002-07-01 2002-10-01 2003-01-01 2003-04-01 2003-07-01 2003-10-01 [13] 2004-01-01 2004-04-01 2004-07-01 2004-10-01 2005-01-01 2005-04-01 [19] 2005-07-01 2005-10-01 2006-01-01 2006-04-01 2006-07-01 2006-10-01 [25] 2007-01-01 2007-04-01 2007-07-01 2007-10-01 2008-01-01 2008-04-01 [31] 2008-07-01 2008-10-01 2009-01-01 2009-04-01 2009-07-01 2009-10-01 36 Levels: 2001-01-01 2001-04-01 2001-07-01 2001-10-01 ... 2009-10-01 Regards, Marc Schwartz On Dec 16, 2013, at 6:35 AM, Dániel Kehl <ke...@ktk.pte.hu> wrote: > Hi, > > try > > x <- seq(as.Date("2001/1/1"),as.Date("2010/1/1"),"3 months") > > best, > daniel > ________________________________________ > Feladó: r-help-boun...@r-project.org [r-help-boun...@r-project.org] ; > meghatalmazó: Pancho Mulongeni [p.mulong...@namibia.pharmaccess.org] > Küldve: 2013. december 16. 13:05 > To: 1248283...@qq.com > Cc: r-help@r-project.org > Tárgy: Re: [R] why there is no quarters? > > Hi, > I also would like to use quarters. I think a work around would be to just > label each record in the dataframe by its quarter. > i.e. you add a factor called 'Quarter' with four levels (Q1 to Q4) for each > row and you assign the level based on the month of the date. > You can easily do this with as.Date and as.character. > > Pancho Mulongeni > Research Assistant > PharmAccess Foundation > 1 Fouché Street > Windhoek West > Windhoek > Namibia > > Tel: +264 61 419 000 > Fax: +264 61 419 001/2 > Mob: +264 81 4456 286 ______________________________________________ R-help@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.