[R] Sum of some months totals

[Frederic Ntirenganya]

I want to compute monthly summaries from daily data. I want to choose which
month to start and how many months to total over.  Default could be to
start in January and total over 3 months.  For the number of rain days the
default threshold is 0.85mm.

I tried to make a function which sum all months not some of months. I will
appreciate any help from you guys. Thanks.
Here is the data and the code I used.

> dput(head(kitale))structure(list(Year = c(1979L, 1979L, 1979L, 1979L, 1979L, 1979L
), Month = c(1L, 1L, 1L, 1L, 1L, 1L), Day = 1:6, Rain = c(0,
0, 0, 0, 0, 0)), .Names = c("Year", "Month", "Day", "Rain"), row.names = c(NA,
6L), class = "data.frame")

here is the function:

total = function(data, threshold = 0.85){
  month_tot=matrix(NA,31,12)
  rownames(month_tot)=as.character(1979:2009)
  colnames(month_tot)=c("Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec")
  raindays=month_tot
  # loop over months and years to get summary statistics
  for (mon in 1:12) {
    rain=data[data[2]==mon,c(1,4)]   # rain just for a specific month
    for (yr in 1979:2009) {
      month_tot[yr-1978,mon]=sum(rain[rain[,1]==yr,2])
      raindays[yr-1978,mon]=sum(rain[rain[,1]==yr,2]>threshold)
    }
  }
  month_tot
}

Regards,

Frederic.



Frederic Ntirenganya
Maseno University,
African Maths Initiative,
Kenya.
Mobile:(+254)718492836
Email: fredo at aims.ac.za
https://sites.google.com/a/aims.ac.za/fredo/

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