This function returns a new raster based on an existing raster and cell numbers for that raster.
The new raster is cropped to the cell numbers provided, and, if values=TRUE has values that are the cell numbers of the original raster.
rasterFromCells(x, cells, values=TRUE)
Raster* object (or a SpatialPixels* or SpatialGrid* object)
vector of cell numbers
Logical. If TRUE, the new RasterLayer has cell values that correspond to the cell numbers of x
Cell numbers start at 1 in the upper left corner, and increase from left to right, and then from top to bottom.
The last cell number equals the number of cells of the Raster* object.