How to write every raster from a list of rasters?

Question

I have created a list of rasters - "norm" and run a several loops. Now I would like to write every created raster from "norm" (containing 1 layer) into one raster, having its specific name.

# I can get the rasters names
rst.names<-c(1:length(norm))
for(i in 1:length(norm)){
    rst.names1<-names(norm[[i]])
    rst.names[[i]]<-rst.names1
    }   

To write and save a rasters I have found a very useful answer on https://stackoverflow.com/questions/14890369/how-to-write-rasters-after-stacking-them

where they use to respond my question (modified):

unst_norm<- unstack(norm)
for(i in 1:lenght(unst_norm)){writeRaster(unst_norm[[i]], file=rst.names[i])}

However if I use "unstack" I have this error:

Error in stats::as.formula(form) : 
argument "form" is missing, with no default

and I can´t find any help for that.

I can use "unlist" instead of "unstack" but it doesn't seem to work...

but I still get an error:

Error in .local(.Object, ...) : Unable to create dataset

Please, any ideas where the problem could be? Or, how to automatically write and save all rasters from raster list?

Answer 1

If you have a list of raster objects with equal extent and resolution, it's probably easiest to stack them first and then use writeRaster with bylayer=TRUE.

For example:

library(raster)

1. Create some dummy data

   L <- setNames(replicate(3, raster(matrix(runif(100), 10))), c('A', 'B', 'C'))
   
   L
   
   # $A
   # class       : RasterLayer 
   # dimensions  : 10, 10, 100  (nrow, ncol, ncell)
   # resolution  : 0.1, 0.1  (x, y)
   # extent      : 0, 1, 0, 1  (xmin, xmax, ymin, ymax)
   # coord. ref. : NA 
   # data source : in memory
   # names       : layer 
   # values      : 0.01015837, 0.9958344  (min, max)
   # 
   # 
   # $B
   # class       : RasterLayer 
   # dimensions  : 10, 10, 100  (nrow, ncol, ncell)
   # resolution  : 0.1, 0.1  (x, y)
   # extent      : 0, 1, 0, 1  (xmin, xmax, ymin, ymax)
   # coord. ref. : NA 
   # data source : in memory
   # names       : layer 
   # values      : 0.01501442, 0.9975531  (min, max)
   # 
   # 
   # $C
   # class       : RasterLayer 
   # dimensions  : 10, 10, 100  (nrow, ncol, ncell)
   # resolution  : 0.1, 0.1  (x, y)
   # extent      : 0, 1, 0, 1  (xmin, xmax, ymin, ymax)
   # coord. ref. : NA 
   # data source : in memory
   # names       : layer 
   # values      : 0.01136738, 0.9983568  (min, max)
   

2. And stack them and write them out to separate tifs

   writeRaster(stack(L), names(L), bylayer=TRUE, format='GTiff')
   

This will write out the three layers to tifs with names defined by the layer names, i.e. A.tif, B.tif, and C.tif.

Alternatively, if the rasters in the list are not of equal extent/res, you can iterate over the list and write each out in turn:

mapply(writeRaster, L, names(L), 'GTiff')

I use mapply above for convenience, since it allows easy passing of layer names as file names.

Answer 2

Another solution would be to create a simple for loop.

for (i in 1:length(L)) {
writeRaster(L[[i]], names(L[[i]]), format='GTiff')
}

The rasters will be saved in the path you specified as working directory