Return a list of extents for each cell in a raster

cellBoundaries.R

cellBoundaries <- function(r, spatial=TRUE) {
  # r: a Raster object
  # spatial: return an sfc object (TRUE) or a list of extents (FALSE)
  require(raster)
  if(isTRUE(spatial)) require(sf)
  ee <- lapply(seq_along(r), function(i) {
    cat(sprintf('\r%0.2f%%', 100*i/ncell(r)))
    e <- extentFromCells(r, i)
    if(isTRUE(spatial)) {
      e <- st_as_sfc(st_bbox(e))
      e <- st_set_crs(e, projection(r))
    }
    e
  })
  if(isTRUE(spatial)) do.call(c, ee) else ee
}

# Can use raster::rasterToPolygons(r) for this, but will only return 
#  polys for non-NA cells, so may need to `r2 <- raster(r); r2[] <- 1` 
#  first.