Function to convert a raster to a data.table

as.data.table.raster.R

as.data.table.raster <- function(x, row.names = NULL, optional = FALSE, 
                                 xy = FALSE, inmem = canProcessInMemory(x, 2), 
                                 ...) {
  stopifnot(require("data.table"))
  if(inmem) {
    v <- as.data.table(raster::as.data.frame(x, row.names=row.names, 
                                             optional=optional, xy=xy, ...))
    coln <- names(x)
    if(xy) coln <- c("x", "y", coln)
    setnames(v, coln)
  } else {
    tr <- blockSize(x)
    l <- lapply(1:tr$n, function(i) {
      DT <- as.data.table(as.data.frame(getValues(x, row = tr$row[i], 
                                                  nrows = tr$nrows[i]), ...))  
      if(xy == TRUE) {
        cells <- cellFromRowCol(x, c(tr$row[i], tr$row[i] + tr$nrows[i] - 1),
                                c(1, ncol(br)))
        coords <- xyFromCell(x, cell = cells[1]:cells[2])
        DT[, c("x", "y") := data.frame(xyFromCell(x, cell = cells[1]:cells[2]))]
     } 
     DT
    })
    v <- rbindlist(l)
    coln <- names(br)
    if(xy) {
     coln <- c("x", "y", coln)
     setcolorder(v, coln)
    }
  }
  v
}

dt_to_raster <- function(dt, CRSobj, filename = NULL) {
  if(any(!c("x", "y") %in% colnames(dt))) {
    stop("dt needs planar coordinates in x, y format")
  }
  coordinates(dt) = ~x+y
  proj4string(dt) <- CRSobj
  gridded(dt) = TRUE
  if(ncol(dt) > 1) {
    dtr <- brick(dt)
  } else {
    dtr <- brick(dt)
  }
  if(!is.null(filename)) dtr <- writeRaster(dtr, filename)
  return(dtr)
}

dt_list_to_raster <- function(base, inlist, CRSobj) {
  dts <- lapply(inlist, function(x) {
    dt <- cbind(base, x)
    dtr <- dt_to_raster(dt, CRSobj = CRSobj)
  })
  if(!is.null(names(inlist))) names(dts) <- names(inlist)
  return(dts)
}

raster_list_to_dt <- function(inlist, base = TRUE) {
  if(base == TRUE) {
    base_dt <- as.data.table.raster(inlist[[1]], xy = TRUE)[, c("x", "y"), 
                                                            with = FALSE]
    base_dt[, ind := 1:nrow(base_dt)]
  }
  dts <- lapply(inlist, function(x) {
    dt <- as.data.table.raster(x)
  })
  if(!is.null(names(inlist))) names(dts) <- names(inlist)
  if(base == TRUE) outlist <- list(base_dt, dts)
  if(base == FALSE) outlist <- dts
  return(outlist)
}