[R] Subsetting a zooreg object using window / subset

[Wesley Roberts]

Dear R users,


I am currently working in subsetting a zooreg() object using either window or subset. I have a solution but it may be a bit cumbersome when I start working with actual data. Your inputs would be greatly appreciated.

Example: I have a zooreg() object that starts in 1997 and ends in 2001. This object contains daily data for the 4 years

aa<-zooreg(1:1825,start=as.Date("1997-01-01"))

My aim is to subset the data according to seasons (Southern Hemisphere) for continuous years: December - January - February (DJF-Summer: 1997-2001), March - April - May (MAM-Autumn: 1997-2001), June - July - August (JJA-Winter: 1997-2001), September - October - November (SON-Spring: 1997-2001) thereby analysing the seasons data only for all years. The example below is only for DJF but I would like to replicate the analysis for each season.

My solution so far uses subset to select the monthly data for each year and then rbind() the results.

bb <- subset(aa, index(aa)>=as.Date("1998-12-01")&index(aa)<=as.Date("1999-02-28"))
cc <- subset(aa, index(aa)>=as.Date("1999-12-01")&index(aa)<=as.Date("2000-02-28"))
dd <- subset(aa, index(aa)>=as.Date("2000-12-01")&index(aa)<=as.Date("2001-02-28"))

ee<- rbind(bb,cc,dd)

The method above appears to do the job just fine except that I have around 30 locations (catchments) each with varying data availability and some with over 20 years worth of data. Ideally I would like to combine the second set of commands into a single command where I specify the start and end year and the months that I am interested in.

Any advice on this matter would be greatly appreciated.

Many thanks and kind regards,
Wesley

Wesley Roberts PhD.
Researcher: Earth Observation
Natural Resources & the Environment (NRE)
CSIR
Tel: +27 (0)21 888-2490
Fax: +27 (0)21 888-2693
skype: roberts-w
 
 



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