Any R package for focal statistics (moving window) within a 3D neighborhood

I am trying to find any R package that can provide me any build-on function
for computing a 3D neighborhood filter or statistics,... (if that already
exists!), or if not, at least any function from a non-spatial R-package
that could be useful to build my function.

Any info about preexisting R packages or any tips how to implement it with
other packages are very very welcome!

The data: 3D point data set (centers of voxels= volumetric pixels) read as
an R data.frame  with 4 columns (x,y,z, and an attribute). Can be big (e.g.
millions rows)

The problem: 1) Evaluate the values of the attribute column for all the
points within a 3D neighborhood from any point (any instance in the
data.frame differing less than  "X" value in X,Y,Z, coordinates). (i.e. A
sort of moving window for a raster but in a 3D neighborhood).

2) Transform the "cell" or 3D point attribute value, if a condition is
fulfilled for any of the 3D neighbors.

Thanks a lot!
Jose Tanago
Lab. of Remote Sensing, Wageningen University