R igraph manual pages

Convert a general graph into a forest

Description

Perform a breadth-first search on a graph and convert it into a tree or forest by replicating vertices that were found more than once.

Usage

unfold_tree(graph, mode = c("all", "out", "in", "total"), roots)

Arguments

graph	The input graph, it can be either directed or undirected.
mode	Character string, defined the types of the paths used for the breadth-first search. “out” follows the outgoing, “in” the incoming edges, “all” and “total” both of them. This argument is ignored for undirected graphs.
roots	A vector giving the vertices from which the breadth-first search is performed. Typically it contains one vertex per component.

Details

A forest is a graph, whose components are trees.

The roots vector can be calculated by simply doing a topological sort in all components of the graph, see the examples below.

Value

A list with two components:

tree	The result, an igraph object, a tree or a forest.
vertex_index	A numeric vector, it gives a mapping from the vertices of the new graph to the vertices of the old graph.

Author(s)

Gabor Csardi csardi.gabor@gmail.com

Examples

g <- make_tree(10) %du% make_tree(10)
V(g)$id <- seq_len(vcount(g))-1
roots <- sapply(decompose(g), function(x) {
            V(x)$id[ topo_sort(x)[1]+1 ] })
tree <- unfold_tree(g, roots=roots)

---