If raster value NA search and extract the nearest non-NA pixel

Question

On extracting values of a raster to points I find that I have several NA\'s, and rather than use a buffer and fun arguments of extra

Answer 1

For a raster stack, use @koekenbakker's solution above, and turn it into a function. A raster stack's @layers slot is a list of rasters, so, lapply it across and go from there.

#new layer
r2 <- raster(ncol=10,nrow=10, xmn=0, xmx=10, ymn=0,ymx=10)
r2[] <- 1:10
r2[sample(1:ncell(r2), size = 25)] <- NA

#make the stack
r_stack <- stack(r, r2)

#a function for sampling
sample_raster_NA <- function(r, xy){
  apply(X = xy, MARGIN = 1, 
        FUN = function(xy) r@data@values[which.min(replace(distanceFromPoints(r, xy), is.na(r), NA))])

}

#lapply to get answers
lapply(r_stack@layers, function(a_layer) sample_raster_NA(a_layer, xy))

Or to be fancy (speed improvements?)

purrr::map(r_stack@layers, sample_raster_NA, xy=xy)

Which makes me wonder if the whole thing can be sped up even more using dplyr...