Focal filter with stars

[michaeldorman]

This is a general question - hope it's appropriate to ask here.

As someone who just started to work with stars (as replacement for raster), I find the raster::focal function the most significant thing missing from stars at the moment.

According to the migration table (#122), raster::focal is marked as "Not present, could be implemented".

I was wondering whether there are any more concrete development paths in mind -
Is it likely that that a focal filter function will be implemented in stars? If not, do you think it makes sense to use a wrapper that transforms stars<->raster and uses raster::focal? Perhaps you are aware of any general focal filtering function in R, which is aimed at array object and thus may work on stars objects as is?

Thanks for the great work - so far enjoyed using stars very much!

[edzer]

After applying this patch, you can try this:

library(stars)
tif = system.file("tif/L7_ETMs.tif", package = "stars")
x1 = read_stars(tif)
foc = function(x, w) {
	raster::as.matrix(raster::focal(raster::raster(x), w))
}
f = st_apply(x1, 3, foc, w = matrix(1, 3, 3))
plot(f)

[michaeldorman]

Nice! I will use this approach, thank you very much for the help and quick reply!

[florisvdh]

I think that the raster::raster(x) part of the above solution should be as(x, "Raster"), i.e. the function provided by stars. It seems that raster::raster() does not yet accept stars objects.

[edzer]

Did you try? Functions passed as argument to st_apply receive sub-arrays, in this case matrices, not (subsetted) stars objects.

[florisvdh]

You are right; my mistake! Thanks for the clarification.