Added fasterizeDT() function, a wrapper for fasterize::fasterize()

As described in an Issue filed at the **fasterize** package's GitHub
repository (ecohealthalliance/fasterize#26),
`fasterize` returns rasters that match the class of their template
raster, not of the field that the user selected to be burned into
them. In addition, when passed a character or a factor field, it does
not -- as would often be desireable -- return a factor-valued raster.

`fasterizeDT()` addresses both of these issues, consistently returning
a raster whose class (and, if a factor, levels) matches that of the
user-selected field in the input polygon object.

In addition, `fasterizeDT()` accepts `sp::SpatialPolygonsDataFrame()`
objects, converting them to `sf::sf()` objects before passing them on
to `fasterize::fasterize()`.

NAMESPACE

@@ -2,11 +2,14 @@
 
 export(cat_to_val)
 export(crosstabDT)
+export(fasterizeDT)
 export(freqDT)
 export(subsDT)
 export(zonalDT)
 exportMethods(freqDT)
 import(data.table, except = shift)
 import(methods)
 import(raster)
+importFrom(fasterize,fasterize)
+importFrom(sf,st_as_sf)
 importFrom(stats,complete.cases)

R/fasterizeDT.R

@@ -0,0 +1,69 @@
+
+##' A front end for
+##' \code{\link[fasterize:fasterize]{fasterize::fasterize()}}, fixing
+##' several of its infelicities.
+##'
+##' @title Fixed up fasterize Function
+##' @param x An \code{sf::sf()} object with a geometry column of
+##'     \code{POLYGON} and/or \code{MULTIPOLYGON} objects or a
+##'     \code{sp::SpatialPolygonsDataFrame} object.
+##' @param raster A raster object. Used as a template for the raster
+##'     output
+##' @param field character. The name of a column in \code{x},
+##'     providing a value for each of the polygons rasterized. If NULL
+##'     (default), all polygons will be given a value of 1.
+##' @param fun \code{?fasterize::fasterize}
+##' @param background Value to put in the cells that are not covered
+##'     by any of the features of x. Default is NA.
+##' @param by \code{?fasterize::fasterize}
+##' @return A raster of the same size, extent, resolution and
+##'     projection as the supplied raster template. Unlike
+##'     \code{\link[fasterize:fasterize]{fasterize::fasterize()}},
+##'     \code{fasterizeDT} returns a raster of the same type as the
+##'     data in the column of \code{x} column selected by the
+##'     \code{field} argument.
+##' @importFrom fasterize fasterize
+##' @importFrom sf st_as_sf
+##' @export
+##' @author Joshua O'Brien
+##' @examples
+##' \dontrun{
+##' }
+fasterizeDT <- function (x,
+                         raster,
+                         field = NULL,
+                         fun = "last",
+                         background = NA_real_,
+                         by = NULL) {
+    if (class(x) == "SpatialPolygonsDataFrame") {
+        x <- st_as_sf(x)
+    }
+    if (is.null(field)) {
+        field <- names(x)[1]
+    }
+    field_class <- class(x[[field]])
+    ## Convert character field to factor
+    if (field_class == "character") {
+        val <- x[[field]]
+        val <- factor(val, levels = sort(unique(val)))
+        x[[field]] <- val
+    }
+    ## Rasterize polygons
+    out_raster <-
+        fasterize(sf = x, raster = raster, field = field,
+                  fun = fun, background = background, by = by)
+    ## Ensure that any RAT attached to output raster is derived from
+    ## input char or factor field
+    if(field_class %in% c("character", "factor")) {
+        lev <- levels(x[[field]])
+        RAT <- data.frame(ID = seq_along(lev), VALUE = lev)
+        ## Silence warning emitted when overwriting a RAT from input
+        ## raster
+        suppressWarnings(levels(out_raster) <- RAT)
+    } else {
+        out_raster@data@isfactor <- FALSE
+        out_raster@data@attributes <- list()
+    }
+    out_raster
+}
+