Loop in R using changing variable to write and name files - r

Question

I am trying to create a loop in R that reads daily values of a netcdf file I have imported and converts them into annual sums, then creates a raster for each year. I have converted the netcdf into an array - this is named Biased_corrected.array in my code below. I am not sure how to include the variable 'year' in my file names as it changes with each iteration of the loop. I have tried using paste but this seems to be where it fails. Any suggestions?
# read in file specifying which days correspond to years
YearsDays <- read.csv("Data\\Years.csv") # a df with 49 obs. of 3 variables (year, start day, and end day
YearsDays[1,2:3] #returns 1 and 366 (the days for year 1972)
YearsDays[2,2:3] #returns 367 and 731 (the days for year 1973)
YearsDays[1,1] #returns 1972
YearsDays[2,1] #returns 1973
counter <- 1
startyear <- YearsDays[1,1]
year <- startyear
while(year < 2021){
#set variables to loop through
startday <- YearsDays[counter,2]
endday <- YearsDays[counter,3]
BC_rain.slice <- Biased_corrected.array[,,startday:endday]
paste(year, "_Annual_rain") <- apply(BC_rain.slice, c(1,2), sum)
#save data in a raster
paste(year, "_rain_r") <- raster(t(paste(year, "_Annual_Rain"), xmn=min(x), xmx=max(x), ymn=min(y), ymx=max(y), crs=WGS84)
# move on to next year
counter <- counter + 1
year <- 1971 + counter
}
EDIT: The working code for anyone interested:
YearsDays <- read.csv("Data\\Years.csv") # a df with 49 obs. of 3 variables (year, start day, and end day
for (idx in seq(nrow(YearsDays))){
#set variables to loop through
year <- YearsDays[idx,1]
startday <- YearsDays[idx,2]
endday <- YearsDays[idx,3]
BC_rain.slice <- Biased_corrected.array[,,startday:endday]
assign(paste(year, "_Annual_rain"),apply(BC_rain.slice, c(1,2), sum))
annual_rain <- apply(BC_rain.slice, c(1,2), sum)
#save data in a raster
assign(paste(year, "_rain_r"),raster(t(annual_rain), xmn=min(x), xmx=max(x), ymn=min(y), ymx=max(y), crs=WGS84))
}

Answer 1

You can't use paste to create a variable name as you've listed. You can enclose it within assign or eval, however it may be easier to instead store your results within a data frame. Below is an example of what I believe you're trying to achieve. I have also replaced your while loop and counter with a for loop iterating over years:
YearsDays <- read.csv("Data\\Years.csv") # a df with 49 obs. of 3 variables (year, start day, and end day
output <- data.frame(year = YearsDays[,1], rain_r = NA)
for (idx in seq(nrow(YearsDays))){
#set variables to loop through
year <- YearsDays[idx,1]
startday <- YearsDays[idx,2]
endday <- YearsDays[idx,3]
BC_rain.slice <- Biased_corrected.array[,,startday:endday]
annual_rain <- apply(BC_rain.slice, c(1,2), sum)
#save data in a raster
output$rain_r[output$year == year] <- raster(t(annual_rain, xmn=min(x), xmx=max(x), ymn=min(y), ymx=max(y), crs=WGS84))
}

Answer 2

How about to replace your part
paste(year, "_Annual_rain") <- apply(BC_rain.slice, c(1,2), sum)
#save data in a raster
paste(year, "_rain_r") <- raster(t(paste(year, "_Annual_Rain"), xmn=min(x), xmx=max(x), ymn=min(y), ymx=max(y), crs=WGS84)
to
txt <- paste0(year, "_Annual_rain <- apply(BC_rain.slice, c(1,2), sum)")
eval(parse(text = txt))
# save data in a raster
txt <- paste0(year, "_rain_r <- raster(t(", year, "_Annual_Rain), xmn=min(x), xmx=max(x), ymn=min(y), ymx=max(y), crs=WGS84)")
eval(parse(text = txt))