addresses tidyverse/ggplot2#2071

when giving coord_sf(..., datum = NA)

Author: edzer

NEWS.md

@@ -1,5 +1,9 @@
 # version 0.5-3
 
+* allow for arith ops on empty `sfc` objects
+
+* have `st_graticule` return an empty `sf` when argument `datum` is `NA`
+
 * export `as_Spatial`, to make it easer for packages to convert `sfc` objects without importing `sf`
 
 * `st_distance` gains a parameter `by_element` to obtain pairwise distances; #437

R/arith.R

@@ -78,15 +78,22 @@ conform = function(vec, m) {
 
 #' @export
 Ops.sfc <- function(e1, e2) {
+
+	if (length(e1) == 0) # empty set
+		return(e1)
+
 	if ((is.matrix(e2) && ncol(e2) == 2) || (is.numeric(e2) && length(e2) == 2))
 		e1 = st_zm(e1) # drop z and/or m
+
 	if (!is.list(e2))
 		e2 = list(e2)
+
 	ret = switch(.Generic,
 		"*" = mapply(function(x, y) { x * unclass(y) }, e1, e2, SIMPLIFY = FALSE),
 		"+" = mapply(function(x, y) { x + unclass(y) }, e1, e2, SIMPLIFY = FALSE),
 		"-" = mapply(function(x, y) { x - unclass(y) }, e1, e2, SIMPLIFY = FALSE),
 		"%%" = mapply(function(x, y) { x %% unclass(y) }, e1, e2, SIMPLIFY = FALSE),
 		stop(paste("operation", .Generic, "not supported")))
+
 	st_sfc(ret, crs = NA_integer_, precision = attr(e1, "precision"))
 }

R/graticule.R

@@ -74,9 +74,12 @@ st_graticule = function(x = c(-180,-90,180,90), crs = st_crs(x),
 	if (is.null(crs))
 		crs = NA_crs_
 
-	if (is.null(datum) || is.na(datum))
+	if (is.null(datum))
 		datum = crs
 
+	if (is.na(datum))
+		return(st_sf(geom = st_sfc()))
+
 	# Get the bounding box of the plotting space, in crs
 	bb = if (inherits(x, "sf") || inherits(x, "sfc") || inherits(x, "sfg"))
 		st_bbox(x)