Write RasterLayer by loop preserving the layer names and grouping models

Question

I have a RasterStack object from witch I need to take some layers into a new RasterStack. To to that I've created a loop. My problem in that I am losing my original layers names in the process. As you will see below, when I take just one of the layers without the loop, the original name are kept.

In addition I also need to group the layers (variables) into models, so I can iterate though the variables inside each model with a bigger loop I'm building.

How do I extract layers from a raster keeping the original layer naming?

Here is some exemple..

## stk1 is the original RasterStack
## stk1 has 3 models in it (.1,.2,.3) each model has 4 variables (day1, day2, day3, day 4)
names(stk1)
[1] "day1.1" "day2.1" "day3.1" "day4.1"
[5] "day1.2" "day2.2" "day3.2" "day4.2"
[9] "day1.3" "day2.3" "day3.3" "day4.3"

Here is the loop i've got running.

## Selecting day2 and day4 from stk1
variables <- as.factor(c("day2.1", "day4.1", 
                         "day2.2", "day4.2",
                         "day2.3", "day4.3"))

for (i in 1:length(variables))
{
  writeRaster(stk1[[i]], filename = paste0("./data/stk1-", variables[i], ".grd"), format = "raster", bylayer = TRUE) # I've tried with and without bylayer.
}

stk1_select  <- stack(list.files("./data/", pattern = ".grd$", full.names = TRUE))
names(stk1_select) **# this names should be exactly as it is in variables**
[1] "day3.1" "day1.1"
[5] "day2.1" "day4.1"
[9] "day4.2" "day2.2"

Extracting one by one does keep the original layer name.

writeRaster(stk1[["day2.1"]], filename = paste0("./data/stk-", "day2.1", ".grd"), format = "raster")
day2.1 <- raster("./data/stk-day2.1.grd")
names(day2.1)
[1] "day2.1"

Finally what I need is like an array of rasters. stk1_select should be modelA( var: day2, day4), modelB (var: da2, day4), modelC (day2, day4)

Answer 1

You have to select which layer you want to save. i in 1:length(variables) select layer[[1]], layer[[2]], ... , layer[[length(variables)]]. The first layer you want to save is not layer[[1]], is layer[[2]], so is necessary to specify each layer name. Here I present you a way to select specific layer into a loop using which() function:

library(raster)

r <- raster()

r[] <- 1

stk1 <- stack(r,r,r,r,r,r,r,r,r,r,r,r)

idx <- paste0('day',rep(1:4,each=3),'.',rep(1:3))

names(stk1) <- idx

variables <- as.factor(c("day2.1", "day4.1", 
                         "day2.2", "day4.2",
                         "day2.3", "day4.3"))

for (i in variables)
{
  writeRaster(stk1[[which(names(s) %in% i)]], filename = paste0("./data/stk1-", i, ".grd"), format = "raster")
}

stk1_select  <- stack(list.files("./data/", pattern = ".grd$", full.names = TRUE))
names(stk1_select)
## [1] "day2.1" "day2.2" "day2.3" "day4.1" "day4.2" "day4.3"

You can also reorder layers to match with the specific position in variables vector:

stk1_reselect <- stk1_select[[match(variables,names(stk1_select))]]
names(stk1_reselect)
## [1] "day2.1" "day4.1" "day2.2" "day4.2" "day2.3" "day4.3"

---

Create stack for each model:

mdls <- paste0('.',1:3,'.grd$')

list.files()

modellist<- lapply(mdls, function(x){stack(list.files("./data/", pattern = x, full.names = TRUE))})