add fortify() method for sfc and sfg (#2685)

Author: yutannihilation

NAMESPACE

@@ -38,6 +38,8 @@ S3method(fortify,glht)
 S3method(fortify,grouped_df)
 S3method(fortify,lm)
 S3method(fortify,map)
+S3method(fortify,sfc)
+S3method(fortify,sfg)
 S3method(fortify,summary.glht)
 S3method(fortify,tbl)
 S3method(ggplot,"function")

R/fortify-spatial.r

@@ -108,3 +108,16 @@ fortify.Line <- function(model, data, ...) {
   df$order <- 1:nrow(df)
   df
 }
+
+
+#' @export
+#' @method fortify sfc
+fortify.sfc <- function(model, data, ...) {
+  sf::st_sf(geometry = model)
+}
+
+#' @export
+#' @method fortify sfg
+fortify.sfg <- function(model, data, ...) {
+  sf::st_sf(geometry = sf::st_sfc(model))
+}