How can I bring rasters into R using a previously defined year in the name

Question

This seems like A simple question but I'm not sure how to phrase it or ask. I want to bring in to r many rasters from many years and instead of typing them all out, I want to be able to define the year and bring in rasters by incorporating that defined year. This way I can copy and paste my code and instead of changing the year in every raster name, I can just change it once where I define the year.

Here is an example. I defined year as 2012 and in r.12 I tried using it to bring in the raster but this didn't work. r.1 is an example of how the rasters are all named.

year <- "2012"

r.12 <- raster("pr_total_mm_CRU_TS40_historical_12_"+year+".tif")
r.1 <- raster("pr_total_mm_CRU_TS40_historical_01_2012.tif")

Answer 1

You could try grep and list.files something along the lines of

rlist <- list.files(getwd(), "tif$")
r <- raster::stack(rlist[grep("2012", rlist)])

Answer 2

To concatenate text to produce the right filename, use the paste0() function:

year <- "2012"
fn <- paste0("pr_total_mm_CRU_TS40_historical_12_", year, ".tif")

r.12 <- raster(fn)

If you have a set of years and months to load, you might want a RasterStack, which could be built:

years <- 2010:2012
months <- 1:12
ym <- expand.grid(months = months, years = years)
ym <- paste(ym$months, ym$years, sep = "_")

rs <- stack(paste0("pr_total_mm_CRU_TS40_historical_", ym, ".tif")

You can refer to each layer (raster) like a list element, e.g. rs[[2]]