Thanks Dr. Gabor, the commands you gave worked.

----------------------------
 ZABLONE OWITI
 GRADUATE STUDENT
College of Atmospheric Science
Nanjing University of Information, Science and Technology
Add: 219 Ning Liu Rd, Nanjing, Jiangsu, 21004, P.R. China
 Tel: +86-25-58731402
Fax: +86-25-58731456 
Mob. 15077895632 
Website:  www.nuist.edu.cn 
====================================================

----------------------------------------

From: "Gabor Grothendieck" <ggrothendieck@gmail.com>
Sent: Wednesday, May 12, 2010 7:15 PM
To: zowiti@ncst.go.ke
Subject: Re: [R] How to extract sum of particular months in a monthly data 
series 

Try this:

library(zoo)
z <- as.zoo(AirPassengers)
time(z) <- as.yearmon(time(z))

ix <- cycle(as.ts(z)) %in% c(3:5, 10:11)
aggregate(z[ix], floor, sum)

or this:

ix <- format(time(z), "%m") %in% c("03", "04", "05", "10", "11")
aggregate(z[ix], floor, sum)

It would be best if next time you posted some sample data.

On Tue, May 11, 2010 at 11:10 PM, Zablone Owiti wrote:
> Dear Users,
>
> I have a monthly data for a number of years(1960-2007) for a number of
> stations and i wish to extract sesonal time-series for the months of
> March-May and October-November for very station. I have read this data 
with
> read.table  in R with stations as columns and time (months) as rows. My
> attempt to aggregate with the zoo package using the function as.yearqtr
> failed since this sums evey three months of the year from January. Is 
there
> away it can be coersed to aggregate particular months as in my case?
>
> Thanks
>
> ----------------------------
>  ZABLONE OWITI
>  GRADUATE STUDENT
> College of Atmospheric Science
> Nanjing University of Information, Science and Technology
> Add: 219 Ning Liu Rd, Nanjing, Jiangsu, 21004, P.R. China
>  Tel: +86-25-58731402
> Fax: +86-25-58731456
> Mob. 15077895632
> Website:  www.nuist.edu.cn
> ====================================================
>
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide 
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

 

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