[R] Counting dates in arbitrary ranges

[Mike Marchywka]

----------------------------------------
> From: simonjkiss at yahoo.ca
> Date: Tue, 18 Jan 2011 02:16:37 -0500
> To: r-help at r-project.org
> Subject: [R] Counting dates in arbitrary ranges
>
> Dear Colleagues,
> I have a data set that looks as below. I'd like to count the number of dates in a series of arbitrary ranges (breaks) i.e. not pre-defined breaks such as months, quarters or years. table(format()) produces ideally formatted output, but table() does not appear to accept arbitrary ranges.
> I also tried converting the dates to numeric and using histogram to try to get the data, but that doesn't work either. Cut appears to accept an arbitrary range, but I could only get it to produce NAs.
>
> Any suggestions? Yours, Simon Kiss
>
> mydata<-list(x=seq(as.Date("2007-05-01"), as.Date("2009-09-10"),"days"), y=seq(as.Date("2007-06-16"), as.Date("2009-11-12"),"days"))
> table(format(mydata[[1]], "%Y"))
> t_1<-hist(as.numeric(mydata[[1]], breaks=c("14056", "14421")))$counts
> cut(mydata[[1]], breaks=c(as.Date("2008-06-26"), ("2009=06-26")))


well, with POSIXct I guess you could do things like this, 
( not sure about POSIXct vs Date but maybe someone would comment.
I tried to remove my typos( note that you left out an as.Date in the cut cmd too etc), 
leaving in informative error messages,
 but this is just a dump of what I tried. I would think the "rx" thing
at the bottom would be of use to you, 


> str(mydata)
List of 2
 $ x:Class 'Date'  num [1:864] 13634 13635 13636 13637 13638 ...
 $ y:Class 'Date'  num [1:881] 13680 13681 13682 13683 13684 ...
> z=as.POSIXct(mydata$x)
> str(z)
 POSIXct[1:864], format: "2007-04-30 19:00:00" "2007-05-01 19:00:00" ...
> w=(z<"2008-05-01 12:34:56")
> length(which(w==TRUE))
[1] 864
> w=(z<as.POSIXct("2008-05-01 12:34:56"))
> length(which(w==FALSE))
[1] 497
> d1=as.POSIXct("2008-05-01 12:34:56")
> str(d1)
 POSIXct[1:1], format: "2008-05-01 12:34:56"
> d2=as.POSIXct("2009-05-01 08:34:56")
> rx=d1:d2
> str(rx)
 int [1:31521601] 1209663296 1209663297 1209663298 1209663299 1209663300 
301 1209663302 1209663303 1209663304 1209663305 ...
> length(rx)
[1] 31521601
> as.POSIXct(rx[10])
Error in as.POSIXct.numeric(rx[10]) : 'origin' must be supplied
> as.POSIXct(rx[10],origin="1970-01-01")
[1] "2008-05-01 18:35:05 CDT"
>














>
>
> *********************************
> Simon J. Kiss, PhD
> Assistant Professor, Wilfrid Laurier University
> 73 George Street
> Brantford, Ontario, Canada
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> Cell: +1 519 761 7606
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