[R] Sum of some months totals

[Frederic Ntirenganya]

Hi Jean,

Thanks for the help!
How can I compute monthly total of rainfall?

I want to compute both monthly total of rainfall and number of raindays. In
below function month_tot is a table and I want to some month. default is 3
months. The loop for quarter is not working and I am wondering why it is
not working.

total = function(data, threshold = 0.85){
  month_tot=matrix(NA,length(unique(data$Year)),12)
  rownames(month_tot)=as.character(unique(data$Year))

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 unique(data$Year)) {
      month_tot[yr-min(unique(data$Year)-1),mon]=sum(rain[rain[,1]==yr,2])
      #print(sum(rain[rain[,1]==yr,2]))

raindays[yr-min(unique(data$Year)-1),mon]=sum(rain[rain[,1]==yr,2]>threshold)
    }
  }
  month_tot
  1:ncol(month_tot)
  #month_tot[,1] + month_tot[,2] + month_tot[,3]
  quarter <-c()
  i = 3
  for (i in 1:ncol(month_tot)){

    quarter[i] = sum(month_tot[,i])
  }
  quarter
}

total(kitale)

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/

On Tue, Apr 14, 2015 at 1:52 PM, Adams, Jean <jvadams at usgs.gov> wrote:

> If you want to calculate the number of days having greater than a certain
> threshold of rain within a range of months, a function like this might
> serve your needs.
>
> raindays <- function(data, monStart=1, monEnd=3, threshold=0.85) {
>   with(data, {
>     selRows <- Month >= monStart & Month <= monEnd & Rain > threshold
>     days <- tapply(selRows, Year, sum)
>     return(days)
>   })
> }
>
> raindays(kitale)
>
> Jean
>
> On Tue, Apr 14, 2015 at 2:46 AM, Frederic Ntirenganya <ntfredo at gmail.com>
> wrote:
>
>> 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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>>
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>
>

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