On Thu, 22 Sep 2011, Gabor Grothendieck wrote:
On Thu, Sep 22, 2011 at 6:48 AM, Wesley Roberts <wrobe...@csir.co.za> wrote:
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.
This gives the season (1 = djf, 2 = mam, 3 = jja, 5 = son):
seas <- as.numeric(format(as.yearqtr(as.yearmon(time(aa)) + 1/12), "%q"))
An alternative route might be to go via the "mon" component of POSIXlt,
e.g.,
as.POSIXlt(time(aa))$mon %in% c(11, 0, 1)
instead of
seas == 1
etc.
and this picks out djf:
aa[seas == 1]
--
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com
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and provide commented, minimal, self-contained, reproducible code.
