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.

## 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.

## 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.

## See also

Other structural.properties:
`bfs()`

,
`component_distribution()`

,
`connect()`

,
`constraint()`

,
`coreness()`

,
`degree()`

,
`dfs()`

,
`distance_table()`

,
`edge_density()`

,
`feedback_arc_set()`

,
`girth()`

,
`is_acyclic()`

,
`is_dag()`

,
`is_matching()`

,
`k_shortest_paths()`

,
`knn()`

,
`reciprocity()`

,
`subcomponent()`

,
`subgraph()`

,
`topo_sort()`

,
`transitivity()`

,
`which_multiple()`

,
`which_mutual()`

## Author

Gabor Csardi csardi.gabor@gmail.com