Attributes are lost in raster after changing extension and resolution in R

Question

I have the following raster:

> modis
class       : RasterLayer 
dimensions  : 1776, 4320, 7672320  (nrow, ncol, ncell)
resolution  : 0.08333333, 0.08333333  (x, y)
extent      : -180, 180, -64, 84  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0 
data source : /Users/maps/MODIS_PANratios.tif 
names       : MODIS_PANratios 
values      : 1, 20  (min, max)
attributes  :
       ID       category
 from:  0               
 to  : 20 Woody savannas

Please note this raster contains categorical attributes.

I want to create a raster stack with modisand a second raster with different resolution and extent:

> rDif
class       : RasterLayer 
dimensions  : 720, 1440, 1036800  (nrow, ncol, ncell)
resolution  : 0.25, 0.25  (x, y)
extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0 
data source : /Users/maps/liuDif.tif 
names       : liuDif 
values      : 0, 4150641  (min, max)

I use project rasterto adapt extent and resolution from modis to rDifto be able to stack both:

modis.new <- projectRaster(from=modis, to=rDif, method="ngb")

The problem is that the new raster has lost its original attributes:

> modis.new
class       : RasterLayer 
dimensions  : 720, 1440, 1036800  (nrow, ncol, ncell)
resolution  : 0.25, 0.25  (x, y)
extent      : -180, 180, -90, 90  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0 
data source : in memory
names       : MODIS_PANratios 
values      : 1, 20  (min, max)

How can I standardise the extent and resolution of two rasters without loosing the original attributes?

Answer 1

As you have multiple setting to standardise the easiest option is spatial_sync_raster from the spatial.tools package.

This will match the extent, resolution, and crs. It does, however, take quite some time. As you have categorical data you need method ="ngb" to set the re sampling to nearest neighbor