Fix 226 Add cactustree layout

NEWS.md

@@ -21,6 +21,9 @@
 * The linear layout has gained a `weight` argument allowing you to set how much
   space each node occupy. Further, the layout now calculates statistics so that
   it can be used in conjunction with `geom_node_tile()` and `geom_node_arc_bar()`
+* New layout added. Cactustree is a hierarchical layout optimised for 
+  hierarchical edge bundling by placing nodes as budding circles on the 
+  periphery of their parent (#226)
 
 # ggraph 2.1.0
 

R/RcppExports.R

@@ -1,6 +1,10 @@
 # Generated by using Rcpp::compileAttributes() -> do not edit by hand
 # Generator token: 10BE3573-1514-4C36-9D1C-5A225CD40393
 
+cactusTree <- function(parent, order, weight, scale, overlap, upright) {
+    .Call('_ggraph_cactusTree', PACKAGE = 'ggraph', parent, order, weight, scale, overlap, upright)
+}
+
 #' Pack circles together
 #'
 #' This function is a direct interface to the circle packing algorithm used by

R/layout_cactustree.R

@@ -0,0 +1,65 @@
+#' Calculate nodes as fractal circle buds
+#'
+#' The cactustree layout is a hierarchical layout optimised for use with
+#' hierarchical edge bundling ([geom_conn_bundle()]). It is a fractal layout
+#' that places node children as circles on the periphery of their parent circle,
+#' each circle scaled by the total weight of their children.
+#'
+#' @note
+#' cactustree is a layout intended for trees, that is, graphs where nodes
+#' only have one parent and zero or more children. If the provided graph does
+#' not fit this format an attempt to convert it to such a format will be made.
+#'
+#' @param graph An `tbl_graph` object
+#'
+#' @param direction The direction of the tree in the graph. `'out'` (default)
+#' means that parents point towards their children, while `'in'` means that
+#' children point towards their parent.
+#'
+#' @param weight An optional node variable to use as weight. If `NULL` all leaf
+#' nodes will be assigned a weight of `1`.
+#'
+#' @param scale_factor A scaling factor for the circles in the layout. The
+#' radius will be calculated as `total_weight ^ scale_factor` with `total_weight`
+#' being the weight of the node and all it's children.
+#'
+#' @param overlap How much is the center of child nodes offset from the
+#' periphery of their parent as a proportion of their own radius.
+#'
+#' @param upright Logical. Should the children of the root only be distributed
+#' around the top half of the root or all the way around.
+#'
+#' @param circular Logical. Should the layout be transformed to a circular
+#' representation. Ignored.
+#'
+#' @return A data.frame with the columns `x`, `y`, `r`, `leaf`, `depth`,
+#' `circular` as well as any information stored as node variables in the
+#' tbl_graph object.
+#'
+#' @references
+#' Dang, T., Forbes, A. (2017). *CactusTree: A Tree Drawing Approach
+#' for Hierarchical Edge Bundling*. 2017 IEEE Pacific Visualization Symposium,
+#' 210-214. https://doi.org/10.1109/PACIFICVIS.2017.8031596
+#'
+#' @family layout_tbl_graph_*
+#'
+layout_tbl_graph_cactustree <- function(graph, direction = "out", weight = NULL, scale_factor = 0.75, overlap = 0.5, upright = FALSE, circular = FALSE) {
+  weight <- enquo(weight)
+  weight <- eval_tidy(weight, .N())
+  if (is.null(weight)) {
+    weight <- as.numeric(degree(graph, mode = direction) == 0)
+  }
+  hierarchy <- tree_to_hierarchy(graph, direction, NULL, weight, NULL)
+  layout <- cactusTree(hierarchy$parent, hierarchy$order, hierarchy$weight, scale_factor, overlap, upright)[-1, ]
+  nodes <- data_frame0(
+    x = layout[, 1],
+    y = layout[, 2],
+    r = layout[, 3],
+    circular = FALSE,
+    leaf = degree(graph, mode = direction) == 0,
+    depth = node_depth(graph, mode = direction)
+  )
+  nodes <- combine_layout_nodes(nodes, as_tibble(graph, active = 'nodes'))
+  attr(nodes, 'graph') <- add_direction(graph, nodes)
+  nodes
+}

R/tbl_graph.R

@@ -84,7 +84,8 @@ prepare_graph <- function(graph, layout, direction = 'out', ...) {
     'dendrogram',
     'treemap',
     'circlepack',
-    'partition'
+    'partition',
+    'cactustree'
   )
   graph_is_treeish <- with_graph(graph, graph_is_tree() || graph_is_forest())
   if (is_hierarchy || (layout == 'auto' && graph_is_treeish)) {

src/RcppExports.cpp

@@ -10,6 +10,22 @@ Rcpp::Rostream<true>&  Rcpp::Rcout = Rcpp::Rcpp_cout_get();
 Rcpp::Rostream<false>& Rcpp::Rcerr = Rcpp::Rcpp_cerr_get();
 #endif
 
+// cactusTree
+NumericMatrix cactusTree(IntegerVector parent, IntegerVector order, NumericVector weight, double scale, double overlap, bool upright);
+RcppExport SEXP _ggraph_cactusTree(SEXP parentSEXP, SEXP orderSEXP, SEXP weightSEXP, SEXP scaleSEXP, SEXP overlapSEXP, SEXP uprightSEXP) {
+BEGIN_RCPP
+    Rcpp::RObject rcpp_result_gen;
+    Rcpp::RNGScope rcpp_rngScope_gen;
+    Rcpp::traits::input_parameter< IntegerVector >::type parent(parentSEXP);
+    Rcpp::traits::input_parameter< IntegerVector >::type order(orderSEXP);
+    Rcpp::traits::input_parameter< NumericVector >::type weight(weightSEXP);
+    Rcpp::traits::input_parameter< double >::type scale(scaleSEXP);
+    Rcpp::traits::input_parameter< double >::type overlap(overlapSEXP);
+    Rcpp::traits::input_parameter< bool >::type upright(uprightSEXP);
+    rcpp_result_gen = Rcpp::wrap(cactusTree(parent, order, weight, scale, overlap, upright));
+    return rcpp_result_gen;
+END_RCPP
+}
 // pack
 NumericMatrix pack(NumericVector areas);
 RcppExport SEXP _ggraph_pack(SEXP areasSEXP) {
@@ -129,6 +145,7 @@ END_RCPP
 }
 
 static const R_CallMethodDef CallEntries[] = {
+    {"_ggraph_cactusTree", (DL_FUNC) &_ggraph_cactusTree, 6},
     {"_ggraph_pack", (DL_FUNC) &_ggraph_pack, 1},
     {"_ggraph_circlePackLayout", (DL_FUNC) &_ggraph_circlePackLayout, 2},
     {"_ggraph_dendrogram_spread", (DL_FUNC) &_ggraph_dendrogram_spread, 7},