# Re: [R] Processing dates and generating sequences of dates

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Mon, 4 Feb 2008 22:38:38 -0500

y <- as.Date(cut(range(my.dates), "years")) + c(0, 364) seq(y[1], y[2], "months")

On Mon, Feb 4, 2008 at 1:00 PM, Gabor Grothendieck <ggrothendieck_at_gmail.com> wrote:
> OK. Here are two zoo solutions and one using only core
> functions.
>
> In the first dd is the first of the month of Jan
> and month of Dec of the first and last year respectively
> so we apply seq.Dates to that.
>
> In the second yr is Jan of the first and Jan of the
> last year as "yearmon" class and we adjust, apply seq and
> convert that to Date.
>
> In the last we convert to POSIXlt and update the internals
> of that object finally converting back to Date and using seq.
>
> library(zoo)
> dd <- as.Date(floor(as.yearmon(range(my.dates))) + c(0, 11/12))
> seq(dd[1], dd[2], by = "month")
>
> library(zoo)
> yr <- floor(as.yearmon(range(my.dates)))
> as.Date(seq(yr[1], yr[2]+11/12, by = 1/12))
>
> dd <- as.POSIXlt(range(my.dates))
> dd\$mon <- c(0, 11)
> dd\$mday <- c(1, 1)
> dd <- as.Date(dd)
> seq(dd[1], dd[2], by = "month")
>
>
> On Feb 4, 2008 12:09 PM, Gavin Simpson <gavin.simpson_at_ucl.ac.uk> wrote:
> > On Mon, 2008-02-04 at 10:48 -0500, Gabor Grothendieck wrote:
> > > Using zoo's yearmon class:
> > >
> > > library(zoo)
> > > my.dates[!duplicated(as.yearmon(my.dates))]
> > >
> > > or, although you seem to disallow this in your question,
> > > this would be an option:
> > >
> > > my.dates[!duplicated(format(my.dates, "%Y-%m"))]
> >
> > Ah, actually, I spoke too soon. Your solutions return the following
> >
> > > my.dates[!duplicated(format(my.dates, "%Y-%m"))]
> > [1] "2005-05-01" "2005-06-01" "2005-07-01" "2005-08-01" "2005-09-01"
> > [6] "2005-10-01" "2005-11-01" "2005-12-01" "2006-01-01" "2006-02-01"
> > [11] "2006-03-01" "2006-04-01" "2006-05-01" "2006-06-01" "2006-07-01"
> > [16] "2006-08-01" "2006-09-01" "2006-10-01" "2006-11-01" "2006-12-01"
> > [21] "2007-01-01" "2007-02-01" "2007-03-01" "2007-04-01" "2007-05-01"
> > [26] "2007-06-01" "2007-07-01"
> >
> > which gives only the months sampled. What I need is a vector of length
> > 36 covering 1st Jan 2005 through 31st Dec 2007 as in (using the seq()
> > call in my original email):
> >
> > > new.dates
> > [1] "2005-01-01" "2005-02-01" "2005-03-01" "2005-04-01" "2005-05-01"
> > [6] "2005-06-01" "2005-07-01" "2005-08-01" "2005-09-01" "2005-10-01"
> > [11] "2005-11-01" "2005-12-01" "2006-01-01" "2006-02-01" "2006-03-01"
> > [16] "2006-04-01" "2006-05-01" "2006-06-01" "2006-07-01" "2006-08-01"
> > [21] "2006-09-01" "2006-10-01" "2006-11-01" "2006-12-01" "2007-01-01"
> > [26] "2007-02-01" "2007-03-01" "2007-04-01" "2007-05-01" "2007-06-01"
> > [31] "2007-07-01" "2007-08-01" "2007-09-01" "2007-10-01" "2007-11-01"
> > [36] "2007-12-01"
> >
> > This just seems a bit kludgy:
> >
> > new.dates <- seq(as.Date(paste(format(min(my.dates), format = "%Y"),
> > "1", "1", sep = "/")),
> > as.Date(paste(format(max(my.dates), format = "%Y"),
> > "12", "31", sep = "/")),
> > by = "months")
> >
> > but perhaps there isn't a better way?
> >
> > Cheers,
> >
> >
> > G
> >
> > >
> > >
> > > On Feb 4, 2008 10:39 AM, Gavin Simpson <gavin.simpson_at_ucl.ac.uk> wrote:
> > > > hits=-2.6 tests=BAYES_00
> > > > X-USF-Spam-Flag: NO
> > > >
> > > > Dear List,
> > > >
> > > > Say I have the following sequence of dates [*]:
> > > >
> > > > start <- as.Date("2005-01-05", format = "%Y-%d-%m")
> > > > end <- as.Date("2007-10-07", format = "%Y-%d-%m")
> > > > my.dates <- seq(start, end, by = "days")
> > > >
> > > > What I would like to generate is a sequence of dates, by month that goes
> > > > from the first day of 2005 (the year of the start date) to the last day
> > > > of 2007 (the year of the end date), so that the output is a vector of 36
> > > > dates containing all months of the three calendar years that the
> > > > sampling spanned.
> > > >
> > > > I could do it via manipulation of dates as so:
> > > >
> > > > new.dates <- seq(as.Date(paste(format(min(my.dates), format = "%Y"),
> > > > "1", "1", sep = "/")),
> > > > as.Date(paste(format(max(my.dates), format = "%Y"),
> > > > "12", "31", sep = "/")),
> > > > by = "months")
> > > >
> > > > And then manipulate that to get only the month and year parts of the 36
> > > > generated dates.
> > > >
> > > > This doesn't seem very elegant to me. Is there a better/easier way than
> > > > converting back and forth between characters and objects of class
> > > > "Date"?
> > > >
> > > > Many thanks,
> > > >
> > > > G
> > > >
> > > > [*] FWIW, my actual application is similar to my.dates, but not sampled
> > > > every day - indeed there are months where there are no samples - and I
> > > > am trying to do a levelplot of the numbers of observations per month,
> > > > per year. Given the following data
> > > >
> > > > dat <- data.frame(temp = rnorm(length(my.dates)),
> > > > my.dates = my.dates)
> > > > dat\$year <- as.numeric(format(dat\$my.dates, format = "%Y"))
> > > > dat\$month <- format(dat\$my.dates, format = "%b")
> > > > dat\$month <- factor(dat\$month, levels = c("Jan","Feb","Mar","Apr",
> > > > "May","Jun","Jul","Aug",
> > > > "Sep","Oct","Nov","Dec"))
> > > >
> > > > I can get a table of the number of observations per month per year via
> > > >
> > > > (obs.yearmon <- with(dat, table(year, month)))
> > > >
> > > > Which when converted to a vector provides what I need for levelplot()'s
> > > > formula method. Now I just need to generate the sequence of 36 months
> > > > ("Jan", "Feb" etc) and years to go with it. The matrix method of
> > > > levelplot works, but I am having to hard code a lot of details that I
> > > > believe the formula method will handle automagically for me.
> > > > --
> > > > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
> > > > Dr. Gavin Simpson [t] +44 (0)20 7679 0522
> > > > ECRC, UCL Geography, [f] +44 (0)20 7679 0565
> > > > Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk
> > > > Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/
> > > > UK. WC1E 6BT. [w] http://www.freshwaters.org.uk
> > > > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
> > > >
> > > > ______________________________________________
> > > > R-help_at_r-project.org mailing list
> > > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > > and provide commented, minimal, self-contained, reproducible code.
> > > >
> > >
> > > ______________________________________________
> > > R-help_at_r-project.org mailing list
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> > > and provide commented, minimal, self-contained, reproducible code.
> > --
> >
> > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
> > Dr. Gavin Simpson [t] +44 (0)20 7679 0522
> > ECRC, UCL Geography, [f] +44 (0)20 7679 0565
> > Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk
> > Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/
> > UK. WC1E 6BT. [w] http://www.freshwaters.org.uk
> > %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
> >
> >
>

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