[R] Year and month from a sequence

[Eric Berger]

Hi Milu,
Jim gave a good solution. Another approach is to use standard packages
and objects.
In particular 'ts' (time series) objects from the stats package, and
'xts' (extensible time-series) objects from the xts package.

library(xts)
# construct dummy data
z <- rnorm(36)
# convert it into a monthly time series starting from January 1861
a <- ts(z,start=c(1861,1),frequency=12)
# create an xts object from 'a'
b <- as.xts(a)

# you can use index(b) to get what you want, e.g.
as.Date(index(b))
#  [1] "1861-01-01" "1861-02-01" "1861-03-01" "1861-04-01"
"1861-05-01" "1861-06-01"
# [7] "1861-07-01" "1861-08-01" "1861-09-01" "1861-10-01" "1861-11-01"
"1861-12-01"
# [13] "1862-01-01" "1862-02-01" "1862-03-01" "1862-04-01"
"1862-05-01" "1862-06-01"
# [19] "1862-07-01" "1862-08-01" "1862-09-01" "1862-10-01"
"1862-11-01" "1862-12-01"
# [25] "1863-01-01" "1863-02-01" "1863-03-01" "1863-04-01"
"1863-05-01" "1863-06-01"
# [31] "1863-07-01" "1863-08-01" "1863-09-01" "1863-10-01"
"1863-11-01" "1863-12-01"

HTH,
Eric






On Wed, Jul 15, 2020 at 1:59 AM Jim Lemon <drjimlemon using gmail.com> wrote:
>
> Hi Milu,
> This is similar to the "birthday age" problem as it is much easier to
> deal with the constant "12 months in a year" rather than the highly
> variable number of days between two dates:
>
> monthno2my<-function(x,startyear=1861,startmonth=2400) {
>  year<-startyear+(x-startmonth)%/%12
>  month<-1+(x-startmonth)%%12
>  return(paste(month.abb[month],year))
> }
>
> Adjust this to suit what sort of output you want (i.e. numeric, date).
>
> Jim
>
> On Wed, Jul 15, 2020 at 8:26 AM Miluji Sb <milujisb using gmail.com> wrote:
> >
> > Dear all,
> > I have a panel dataset with a large number of groups (200K+) with a
> > sequence representing the month of the observations (2400 - 4139). The data
> > is from January 1861 to December 2005.
> > My goal is to extract the corresponding month and year for each observation.
> >
> > I tried the following;
> > x$dt <- seq(from=as.Date("1861-01-01"),by='1 month',length=209000)
> >
> > However, the end date is clearly out of the range. I would like to convert
> > the month number (2400 - 4139) to January 1861 to December 2005 by ID. How
> > can I achieve this? Any help will be highly appreciated.
> >
> > Best,
> >
> > Milu
> >
> >         [[alternative HTML version deleted]]
> >
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