Styjun

I have a 3-dimensional array of daily precipitation data [lon, lat, 365] and a 3-dimension file of sowing date [lon, lat, 30]. One sowing for each year on a grid cell. I have a code (given below) to extract season total (sowing to harvest) precipitation on each grid cell.

BUT, now I want to extract precipitation values only from day 30-60 after sowing date on each grid cell (i.e. sowing = day 157 on x,y grid cell for Kharif season and day 305 is sowing date for rabi crop on x, y grid cell). The result would be a 3- dimensional array of 30 days after sowing date [lon, lat, 30days].
I need different windows of days after sowing i.e. day 30-60, 80-100. Sowing date could be different in each grid cell so day 30 after sowing can be different in different grid cells but the length of days (day 30- 60) should be same. any help to select specific days length within the season based on sowing (sdate) and harvest (hdate) files is highly appreciated please

I have tried "by" function to extract 30 days precipitation data within the season from an array of precipitation with 377 176 376 dimensions. for each grid cell, sowing and harvest dates are different, and i tried to extract total precipitation data for 30 days after sowing. i used SDATE [dim(sdate)= 377 176 30] file as index but having error :
[1] 1982
Error in tapply(seq_len(22L), list(sdate[year] = 305L), function (x) :
arguments must have same length
In addition: Warning message:
In sdate[year - 1]:c(326:340) :
numerical expression has 15 elements: only the first used

#precipitation aray
prec<-array(0,dim=nyear)

for (year in c(2:30)) #first year not, because growing season might have started in year 0

 print(year+1980)
 inputprec.file<-paste("E:/Paper_2018/Prec/","prec_",1980+year,".nc",sep="")
 inputprec.file.previous<-paste("E:/Paper_2018/Prec/","prec_",1980+year-1,".nc",sep="")

 nc<-nc_open(inputprec.file)
 lons<-ncvar_get(nc,"longitude")
 lats<-ncvar_get(nc,"latitude")
 val<-ncvar_get(nc,"pr")
 nc_close(nc)

 x<-which(abs(lons-lon)<0.01)
 y<-which(abs(lats-lat)<0.01)
 #for kharif season harvest date (260) is > sowing (157)

 if(hdate[year]>sdate[year])
 
 prec[year]<-sum(val[x,y,sdate[year]:hdate[year]]) # season total 
 else

 
#for Rabi sowing start in November and harvets occurs in March-April next year
 prec[year]<-sum(val[x,y,1:hdate[year]]) # code to extract winter season total precipitation from sdate: hdate spans over two years (1982-1983)
 # nc<-nc_open(inputprec.file.previous)
 # val<-ncvar_get(nc,"pr")
 # nc_close(nc)
 prec[year]<-prec[year]+sum(val[x,y,sdate[year-1]:365])