R: Convert a general graph into a forest

unfold_tree {igraph} | R Documentation

## 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)

[Package igraph version 1.2.6 Index]