[R] given a mid-month date, get the month-end date

[Spencer Graves]

	  If you work much with time data and time series data and you have not 
already mastered the "zoo" package, you may be interested in a small 
testimonial from one unfamiliar with the names of Achim Zeileis and 
Gabor Grothendieck two years ago:  The package itself seems to have many 
useful features, filling an important gap in other capabilities, AND 
vignette("zoo") makes it relatively easy to learn.

	  Those unfamiliar with vignettes in R may wish to know that the command

	> (zoo.vignette <- vignette("zoo"))

will open an Adobe Acrobat file containing a narrative overview of the 
package's capabilities.  The R commands used in the file can be easily 
obtained in a script file after this command via

	  > edit(zoo.vignette)

in RGui;  this should open the R comands in an editor script window. 
This may not have the desired effect in XEmacs, which I use.  Instead, I 
use the following:

	  > Stangle(zoo.vignette$file)

This writes the R commands to file zoo.R in the working directory.  From 
there, I then use menu File -> Open -> “zoo.R”.

	  hope this helps.
	  Spencer Graves
p.s.  In case it's not completely obvious from the above, I wish to here 
extend my thanks and complements to Achim Zeileis and Gabor Grothendieck 
for a great package with good documentation.

Gabor Grothendieck wrote:

> The zoo package has a yearmon class with as methods which can be
> used:
> 
> library(zoo)
> dd <- Sys.Date()  # test data
> 
> as.Date(as.yearmon(dd), frac = 1)
> 
> as.yearmon converts the "Date" class date to a year and month of
> class "yearmon" dropping the day and representing it internally in
> a way consistent with "ts" class.
> 
> as.Date above then converts it back to "Date" class.
> Since yearmon dates have no day (they are just a year and
> a month) the frac argument is used to indicate what fraction
> of the month to use as the day of the month so frac = 0 (the
> default) would give the beginning of the month) and frac = 1
> gives the end.
> 
> On 12/19/05, t c <quantpm at yahoo.com> wrote:
> 
>> I have a vector of dates.
>>
>> I wish to find the month end date for each.
>>
>> Any suggestions?
>>
>> e.g.
>>
>> For 12/15/05, I want 12/31/05,
>>
>> For 10/15/1995, I want 10/31/1995, etc
>>
>>
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>>
>>
>>
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> 
> 
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-- 
Spencer Graves, PhD
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