R: How to standardise extent of rasters for raster stack

Question

So I'm trying to build a raster stack of 7 variables. In ArcMap I've already standardised resolution and CRS, and I tried to standardise extent and column/row number by extracting by mask with a polygon of the study area. Despite this, extent and column/row number still varies.

Originally I skipped over this issue using quick=TRUE when building the raster stack, but since doing that will create more problems later I decided to try to sort it out now. I've tried using the solution posted here, and ended up with this code:

var_files <- list.files(file.path("D:/OneDrive/Diss/final_layers/"),
                        pattern="tif$", full.names = TRUE)
r.var <- list()
for(i in var_files) {
  ras <- try( raster(i) )
  r.var[i] <- data.frame(name = i, nrow=nrow(ras), ncol=ncol(ras), res=res(ras)[1],               
                         proj=proj4string(ras), xmin=extent(ras)[1],             
                         xmax=extent(ras)[2], ymin=extent(ras)[3],                     
                         ymax=extent(ras)[4])
}
do.call("rbind", var_files)
var_stack <- stack(var_files)
plot(var_stack)

And then I get these warnings after the loop:

In addition: Warning messages:
1: In r.var[i] <- data.frame(name = i, nrow = nrow(ras), ncol = ncol(ras),  :
  number of items to replace is not a multiple of replacement length
2: In r.var[i] <- data.frame(name = i, nrow = nrow(ras), ncol = ncol(ras),  :
  number of items to replace is not a multiple of replacement length
3: In r.var[i] <- data.frame(name = i, nrow = nrow(ras), ncol = ncol(ras),  :
  number of items to replace is not a multiple of replacement length
4: In r.var[i] <- data.frame(name = i, nrow = nrow(ras), ncol = ncol(ras),  :
  number of items to replace is not a multiple of replacement length
5: In r.var[i] <- data.frame(name = i, nrow = nrow(ras), ncol = ncol(ras),  :
  number of items to replace is not a multiple of replacement length
6: In r.var[i] <- data.frame(name = i, nrow = nrow(ras), ncol = ncol(ras),  :
  number of items to replace is not a multiple of replacement length
7: In r.var[i] <- data.frame(name = i, nrow = nrow(ras), ncol = ncol(ras),  :
  number of items to replace is not a multiple of replacement length

And this error after do.call:

Error in do.call("rbind", var_files) : second argument must be a list

Answer 1

In the end the solution was absurdly simple - I just made the stack using quick=TRUE, then cropped the stack rasters by the extent of an ESRI shapefile I'd converted to a SpatialPolygonDataFrame. So after the conversion the code was simply:

crop_area <- extent(poly)
var_brick <- crop(var_stack, crop_area)

This gave me a RasterBrick which I could plot without any errors, so I assume it should be fine now.