Fix #58 add h tree

NAMESPACE

@@ -324,6 +324,7 @@ importFrom(igraph,as.undirected)
 importFrom(igraph,as_edgelist)
 importFrom(igraph,bfs)
 importFrom(igraph,components)
+importFrom(igraph,count_components)
 importFrom(igraph,degree)
 importFrom(igraph,delete_edges)
 importFrom(igraph,delete_vertex_attr)

NEWS.md

@@ -26,6 +26,7 @@
   periphery of their parent (#226)
 * Updated layout functions from the graphlayouts package to support grouped and
   constrained versions (centrality, focus, and stress layouts)
+* Added H Tree layout for binary trees (#58)
 
 # ggraph 2.1.0
 

R/RcppExports.R

@@ -52,6 +52,10 @@ dendrogram_spread <- function(graph, starts, y, leaf, repel, pad, ratio) {
     .Call('_ggraph_dendrogram_spread', PACKAGE = 'ggraph', graph, starts, y, leaf, repel, pad, ratio)
 }
 
+hTree <- function(parent, order) {
+    .Call('_ggraph_hTree', PACKAGE = 'ggraph', parent, order)
+}
+
 partitionTree <- function(parent, order, weight, height) {
     .Call('_ggraph_partitionTree', PACKAGE = 'ggraph', parent, order, weight, height)
 }

R/ggraph.R

@@ -83,6 +83,8 @@
 #'   \item{`unrooted`}{Draws unrooted trees based on equal angle with optional
 #'   equal daylight modification. See [layout_tbl_graph_unrooted()] for further
 #'   details}
+#'   \item{`htree`}{Draws binary trees as a space filling fractal. See
+#'   [layout_tbl_graph_htree()] for further details}
 #' }
 #'
 #' Alternatively a matrix or a data.frame can be provided to the `layout`

R/layout_htree.R

@@ -0,0 +1,52 @@
+#' Layout binary trees in a fractal H formation
+#'
+#' This is a spac efficient layout only useful for binary trees. It is fractal
+#' and works by offsetting child nodes from their parent either horizontally or
+#' vertically depending on depth. The offset is decreased at each step by a
+#' factor of the square root of 2.
+#'
+#' @note
+#' H Tree 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 sort.by The name of a node variable to sort the nodes by.
+#'
+#' @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 circular Logical. Should the layout be transformed to a circular
+#' representation. Ignored
+#'
+#' @return A data.frame with the columns `x`, `y`, `leaf`, `depth`, `circular`
+#' as well as any information stored as node variables in the tbl_graph object.
+#'
+#' @family layout_tbl_graph_*
+#'
+#' @importFrom igraph degree count_components
+#'
+layout_tbl_graph_htree <- function(graph, sort.by = NULL, direction = 'out', circular = FALSE) {
+  if (any(degree(graph, mode = direction) > 2)) {
+    cli::cli_abort("H-Tree layouts can only be used with binary trees")
+  }
+  if (count_components(graph, "weak") != 1) {
+    cli::cli_abort("H-Tree layouts can only be used with fully connected graphs")
+  }
+  sort.by <- enquo(sort.by)
+  sort.by <- eval_tidy(sort.by, .N())
+  hierarchy <- tree_to_hierarchy(graph, direction, sort.by, NULL)
+  layout <- hTree(hierarchy$parent, hierarchy$order)[-1, ]
+  nodes <- data_frame0(
+    x = layout[, 1],
+    y = layout[, 2],
+    circular = FALSE
+  )
+  nodes$leaf <- degree(graph, mode = direction) == 0
+  nodes$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

@@ -85,7 +85,8 @@ prepare_graph <- function(graph, layout, direction = 'out', ...) {
     'treemap',
     'circlepack',
     'partition',
-    'cactustree'
+    'cactustree',
+    'htree'
   )
   graph_is_treeish <- with_graph(graph, graph_is_tree() || graph_is_forest())
   if (is_hierarchy || (layout == 'auto' && graph_is_treeish)) {

_pkgdown.yml

@@ -75,6 +75,7 @@ reference:
       - layout_tbl_graph_treemap
       - layout_tbl_graph_partition
       - layout_tbl_graph_cactustree
+      - layout_tbl_graph_htree
       - layout_tbl_graph_matrix
       - layout_tbl_graph_hive
       - layout_tbl_graph_fabric

src/RcppExports.cpp

@@ -66,6 +66,18 @@ BEGIN_RCPP
     return rcpp_result_gen;
 END_RCPP
 }
+// hTree
+NumericMatrix hTree(IntegerVector parent, IntegerVector order);
+RcppExport SEXP _ggraph_hTree(SEXP parentSEXP, SEXP orderSEXP) {
+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_result_gen = Rcpp::wrap(hTree(parent, order));
+    return rcpp_result_gen;
+END_RCPP
+}
 // partitionTree
 NumericMatrix partitionTree(IntegerVector parent, IntegerVector order, NumericVector weight, NumericVector height);
 RcppExport SEXP _ggraph_partitionTree(SEXP parentSEXP, SEXP orderSEXP, SEXP weightSEXP, SEXP heightSEXP) {
@@ -149,6 +161,7 @@ static const R_CallMethodDef CallEntries[] = {
     {"_ggraph_pack", (DL_FUNC) &_ggraph_pack, 1},
     {"_ggraph_circlePackLayout", (DL_FUNC) &_ggraph_circlePackLayout, 2},
     {"_ggraph_dendrogram_spread", (DL_FUNC) &_ggraph_dendrogram_spread, 7},
+    {"_ggraph_hTree", (DL_FUNC) &_ggraph_hTree, 2},
     {"_ggraph_partitionTree", (DL_FUNC) &_ggraph_partitionTree, 4},
     {"_ggraph_cut_lines", (DL_FUNC) &_ggraph_cut_lines, 9},
     {"_ggraph_pathAttr", (DL_FUNC) &_ggraph_pathAttr, 2},