[R] Adding 1 month to a dataframe column

[Gabor Grothendieck]

Try this:

  # example data - Jan 31/00, Feb 29/00, Mar 31/00, ..., Dec 31/00
  d <- seq(as.Date("2000-02-01"), by = "month", length = 12) - 1
  d

  # find beginning of next month
  nextmon  <- function(d) as.Date(cut(as.Date(cut(d, "month")) + 32, "month"))

  # add number of days from start of current month to next month
  nextmon(d) + as.POSIXlt(d)$mday - 1

  # If all your dates are at month end and  you want the plus 1 month
  # to be at month end too then replace last line with:

  nextmon(nextmon(d)) - 1

The last one can be done even more easily with as.yearmon from zoo.
It converts the dates to a year plus 0 for jan, 1/12 for feb, etc. Also,
as.Date.yearmon(..., frac = 1) converts back from yearmon class to
Date class using end of month for the result so:

  library(zoo)
  as.Date(as.yearmon(d) + 1/12, frac = 1)


On Thu, Sep 18, 2008 at 12:24 PM,  <ANGELO.LINARDI at bancaditalia.it> wrote:
> Dear R experts,
> I have a problem in modifying one column of a dataframe with a datatime
> format using a datetime operator.
> Here is my dataframe A:
>
>     DATACONT PROVINCIA VALORE
> 1  2007-12-31        MI      1
> 2  2007-12-31        PV      2
> 3  2007-12-31        NA      3
> 4  2007-12-31        MI      4
> 5  2007-12-31        RM      5
> 6  2007-12-31        RM      6
> 7  2007-12-31        MI      7
> 8  2008-12-31        MI     11
> 9  2008-12-31        PV     12
> 10 2008-12-31        NA     13
> 11 2008-12-31        MI     14
> 12 2008-12-31        RM     15
> 13 2008-12-31        RM     16
> 14 2008-12-31        MI     17
> 15 2006-12-31        MI     -9
> 16 2006-12-31        PV     -8
> 17 2006-12-31        NA     -7
> 18 2006-12-31        MI     -6
> 19 2006-12-31        RM     -5
> 20 2006-12-31        RM     -4
> 21 2006-12-31        MI     -3
>
> Suppose I want to shift all dates by 1 year, obtaining the following
> dataframe B:
>
> DATACONT PROVINCIA VALORE
> 1  2008-12-31        MI      1
> 2  2008-12-31        PV      2
> 3  2008-12-31        NA      3
> 4  2008-12-31        MI      4
> 5  2008-12-31        RM      5
> 6  2008-12-31        RM      6
> 7  2008-12-31        MI      7
> 8  2009-12-31        MI     11
> 9  2009-12-31        PV     12
> 10 2009-12-31        NA     13
> 11 2009-12-31        MI     14
> 12 2009-12-31        RM     15
> 13 2009-12-31        RM     16
> 14 2009-12-31        MI     17
> 15 2007-12-31        MI     -9
> 16 2007-12-31        PV     -8
> 17 2007-12-31        NA     -7
> 18 2007-12-31        MI     -6
> 19 2007-12-31        RM     -5
> 20 2007-12-31        RM     -4
> 21 2007-12-31        MI     -3
>
> I tried with seq.Date:
> seq.Date(a$"DATA",by="1 month",len=2)[2]
>
> but it works only for single values (the "from" must have length=1).
> Any hints ?
> Thank you in advance
>
> Angelo Linardi
>
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