Function to return values (velox raster)

Question

I'm using the new velox extract function to speed up raster extraction by shapefiles.

The old raster package's extract function by default returned a list of cell values, for example when you use the below format:

val.list <- raster::extract(raster, shapefile)

The new velox package requires a fun= argument and I can't for the life of me get it to return the values:

vx.raster <- velox(raster)
vx.vals <- vx.raster$extract(shapefile, fun=??????)

I have tried:
fun=values (returns error Error during wrapup: unable to find an inherited method for function 'values' for signature 'numeric'
fun=function(x){values(x)} (same error as above)

I get fun=sum, fun=mean to work just fine. Whats up with values? Am I just missing something obvious about a numeric vector and returning a values list (which I feel is the most likely case)?

Thank you!

Answer 1

Simply try this snippet

vx.raster$crop(shapefile).

Answer 2

The development version of velox (on github) now allows returning 'raw' raster values from a VeloxRaster_extract query. Just set the fun argument to NULL.

Here's an example:

library(devtools)
install_github('hunzikp/velox')
library(velox)

## Make VeloxRaster with two bands
set.seed(0)
mat1 <- matrix(rnorm(100), 10, 10)
mat2 <- matrix(rnorm(100), 10, 10)
vx <- velox(list(mat1, mat2), extent=c(0,1,0,1), res=c(0.1,0.1),
        crs="+proj=longlat +datum=WGS84 +no_defs")

## Make SpatialPolygons
library(sp)
library(rgeos)
coord <- cbind(0.5, 0.5)
spoint <- SpatialPoints(coords=coord)
spols <- gBuffer(spgeom=spoint, width=0.5)

## Extract
vx$extract(sp=spols, fun=NULL)$buffer
#             [,1]        [,2]
# [1,]  1.27242932  0.04658030
# [2,]  0.41464143 -1.13038578
# [3,] -1.53995004  0.57671878
#  etc....