Closes plotly#1614. Implemented to_basic for the geom_alluvium and geom_stratum

Author: moutikabdessabour

R/layers2traces.R

@@ -613,6 +613,35 @@ to_basic.GeomQuantile <- function(data, prestats_data, layout, params, p, ...){
   dat
 }
 
+#' @export
+to_basic.GeomStratum <- function (data, ...) {
+  to_basic.GeomRect(data, ...)
+}
+
+#' @export 
+to_basic.GeomAlluvium <- function (data, ...) {
+  prefix_class(transform_alluvium(data), "GeomPolygon") 
+}
+
+# tranform the alluvium data into the corresponding polygons
+transform_alluvium <- function(data) {
+  data <- data[order(data$x), ]
+  
+  if(unique(data$colour) == 0) data$colour <- NULL
+  
+  unused_aes <- ! names(data) %in% c("x", "y", "ymin", "ymax")
+
+  row_number <- nrow(data)
+
+  data_rev <- data[nrow(data):1L, ]
+
+  structure(rbind(
+    cbind(x = data$x, y = data$ymin, data[unused_aes]),
+    cbind(x = data$x[row_number], y = data$ymin[row_number], data[row_number, unused_aes]),
+    cbind(x = data_rev$x, y = data_rev$ymax, data_rev[unused_aes])
+  ), class = class(data))
+}
+
 #' @export
 to_basic.default <- function(data, prestats_data, layout, params, p, ...) {
   data