[R] difference between 2 dates: IN MONTHS the way Motherscompute it

[Francisco J. Zagmutt]

Gabor, please correct me if I am wrong but shouldn't you use as.Date to 
change the date string to a "Date" class before you call as.yearmon?  i.e.

12* 
as.numeric(as.yearmon(as.Date("2006-03-07"))-as.yearmon(as.Date("2006-02-07")))

That returns 1 in Windows XP

Regards

Francisco



>From: "Gabor Grothendieck" <ggrothendieck at gmail.com>
>To: "Smith, Phil" <pzs6 at cdc.gov>
>CC: r-help at stat.math.ethz.ch
>Subject: Re: [R] difference between 2 dates: IN MONTHS the way 
>Motherscompute it
>Date: Fri, 10 Mar 2006 13:38:12 -0500
>
>zoo has the "yearmon" class which will convert a date to a year +
>0/12 to 11/12 to represent the month, disregarding the day, so:
>
>library(zoo)
>12 * as.numeric((as.yearmon("2006-03-07") - as.yearmon("2006-02-06"))) # 1
>
>On 3/10/06, Smith, Phil <pzs6 at cdc.gov> wrote:
> > Hi R-people:
> >
> > I need a function to compute the number of months between 2 dates, in 
>the same way a mother would do it.
> >
> > For example, if a kid is born on February 6, the number of months 
>between that date and March 7 is exactly 1 month, although it is only 29 
>days.
> >
> > Thank you!
> > Phil Smith
> > CDC
> >
> >
> >
> >
> >        [[alternative HTML version deleted]]
> >
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