How to get the number of pixel with a given value from a RasterLayer in R?

Question

I'm working with Corine Land cover data. I want to assess the number of pixels with any forest value (311, 312, 313, 321, 322, 323, 324) of two reference years. That's wat I did:

clc00 <- raster("CLC2000ACC_V2018_20.tif")
> clc00
class      : RasterLayer 
dimensions : 46000, 65000, 2.99e+09  (nrow, ncol, ncell)
resolution : 100, 100  (x, y)
extent     : 9e+05, 7400000, 9e+05, 5500000  (xmin, xmax, ymin, ymax)
crs        : +proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs 
source     : CLC2000ACC_V2018_20.tif 
names      : CLC2000ACC_V2018_20 
values     : 111, 999  (min, max)
attributes :
        ID  COUNT CLC_CODE              LABEL1       LABEL2                  LABEL3   R   G   B      RED GREEN     BLUE
 from: 111 777883      111 Artificial surfaces Urban fabric Continuous urban fabric 230   0  77 0.901961     0 0.301961
  to : 999  40471      999        999 (Nodata) 999 (Nodata)            999 (Nodata) 255 255 255 1.000000     1 1.000000

> forest_ID <- c(311, 312, 313, 321, 322, 323, 324)
> clc_forest00 <- clc00%in%forest_ID
> clc_forest00
class      : RasterLayer 
dimensions : 46000, 65000, 2.99e+09  (nrow, ncol, ncell)
resolution : 100, 100  (x, y)
extent     : 9e+05, 7400000, 9e+05, 5500000  (xmin, xmax, ymin, ymax)
crs        : +proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000 +ellps=GRS80 +units=m +no_defs 
source     : r_tmp_2022-02-02_152455_11840_94056.grd 
names      : layer 
values     : 0, 1  (min, max)

how can I get the amount of pixels of which value=1 is true?

Answer 1

If the raster values can fit into memory, then:

> sum(values(clc_forest00), na.rm=TRUE)
[1] 148558

Your raster is pretty large so this might fail. In which case it might be possible to loop over chunks of the raster using getValues or blocks using getValuesBlock.

> canProcessInMemory(clc_forest00)
[1] TRUE

might let you know if the raster is too big for all the values.