Respect the presence of holes in calculated contours (#3705)

Author: thomasp85

R/stat-contour.r

@@ -106,7 +106,7 @@ StatContourFilled <- ggproto("StatContourFilled", Stat,
 
     isobands <- xyz_to_isobands(data, breaks)
     names(isobands) <- pretty_isoband_levels(names(isobands))
-    path_df <- iso_to_path(isobands, data$group[1])
+    path_df <- iso_to_polygon(isobands, data$group[1])
 
     path_df$level <- factor(path_df$level, levels = names(isobands))
 
@@ -197,12 +197,12 @@ isoband_z_matrix <- function(data) {
   raster
 }
 
-#' Convert the output of isoband functions
+#' Convert the output of isolines functions
 #'
-#' @param iso the output of [isoband::isolines()] or [isoband::isobands()]
+#' @param iso the output of [isoband::isolines()]
 #' @param group the name of the group
 #'
-#' @return A data frame that can be passed to [geom_path()] or [geom_polygon()].
+#' @return A data frame that can be passed to [geom_path()].
 #' @noRd
 #'
 iso_to_path <- function(iso, group = 1) {
@@ -235,6 +235,45 @@ iso_to_path <- function(iso, group = 1) {
   )
 }
 
+#' Convert the output of isoband functions
+#'
+#' @param iso the output of [isoband::isobands()]
+#' @param group the name of the group
+#'
+#' @return A data frame that can be passed to [geom_polygon()].
+#' @noRd
+#'
+iso_to_polygon <- function(iso, group = 1) {
+  lengths <- vapply(iso, function(x) length(x$x), integer(1))
+
+  if (all(lengths == 0)) {
+    warn("stat_contour(): Zero contours were generated")
+    return(new_data_frame())
+  }
+
+  levels <- names(iso)
+  xs <- unlist(lapply(iso, "[[", "x"), use.names = FALSE)
+  ys <- unlist(lapply(iso, "[[", "y"), use.names = FALSE)
+  ids <- unlist(lapply(iso, "[[", "id"), use.names = FALSE)
+  item_id <- rep(seq_along(iso), lengths)
+
+  # Add leading zeros so that groups can be properly sorted
+  groups <- paste(group, sprintf("%03d", item_id), sep = "-")
+  groups <- factor(groups)
+
+  new_data_frame(
+    list(
+      level = rep(levels, lengths),
+      x = xs,
+      y = ys,
+      piece = as.integer(groups),
+      group = groups,
+      subgroup = ids
+    ),
+    n = length(xs)
+  )
+}
+
 #' Pretty isoband level names
 #'
 #' @param isoband_levels `names()` of an [isoband::isobands()] object.