# R igraph manual pages

Use this if you are using igraph from R

### Description

Breadth-first search is an algorithm to traverse a graph. We start from a root vertex and spread along every edge “simultaneously”.

### Usage

bfs(graph, root, neimode = c("out", "in", "all", "total"),
unreachable = TRUE, restricted = NULL, order = TRUE,
rank = FALSE, father = FALSE, pred = FALSE, succ = FALSE,
dist = FALSE, callback = NULL, extra = NULL,
rho = parent.frame())


### Arguments

 graph The input graph. root Numeric vector, usually of length one. The root vertex, or root vertices to start the search from. neimode For directed graphs specifies the type of edges to follow. ‘out’ follows outgoing, ‘in’ incoming edges. ‘all’ ignores edge directions completely. ‘total’ is a synonym for ‘all’. This argument is ignored for undirected graphs. unreachable Logical scalar, whether the search should visit the vertices that are unreachable from the given root vertex (or vertices). If TRUE, then additional searches are performed until all vertices are visited. restricted NULL (=no restriction), or a vector of vertices (ids or symbolic names). In the latter case, the search is restricted to the given vertices. order Logical scalar, whether to return the ordering of the vertices. rank Logical scalar, whether to return the rank of the vertices. father Logical scalar, whether to return the father of the vertices. pred Logical scalar, whether to return the predecessors of the vertices. succ Logical scalar, whether to return the successors of the vertices. dist Logical scalar, whether to return the distance from the root of the search tree. callback If not NULL, then it must be callback function. This is called whenever a vertex is visited. See details below. extra Additional argument to supply to the callback function. rho The environment in which the callback function is evaluated.

### Details

The callback function must have the following arguments:

graph

The input graph is passed to the callback function here.

data

A named numeric vector, with the following entries: ‘vid’, the vertex that was just visited, ‘pred’, its predecessor, ‘succ’, its successor, ‘rank’, the rank of the current vertex, ‘dist’, its distance from the root of the search tree.

extra

The extra argument.

See examples below on how to use the callback function.

### Value

A named list with the following entries:

 root Numeric scalar. The root vertex that was used as the starting point of the search. neimode Character scalar. The neimode argument of the function call. Note that for undirected graphs this is always ‘all’, irrespectively of the supplied value. order Numeric vector. The vertex ids, in the order in which they were visited by the search. rank Numeric vector. The rank for each vertex. father Numeric vector. The father of each vertex, i.e. the vertex it was discovered from. pred Numeric vector. The previously visited vertex for each vertex, or 0 if there was no such vertex. succ Numeric vector. The next vertex that was visited after the current one, or 0 if there was no such vertex. dist Numeric vector, for each vertex its distance from the root of the search tree.

Note that order, rank, father, pred, succ and dist might be NULL if their corresponding argument is FALSE, i.e. if their calculation is not requested.

### Author(s)

Gabor Csardi csardi.gabor@gmail.com

dfs for depth-first search.

### Examples


## Two rings
bfs(make_ring(10) %du% make_ring(10), root=1, "out",
order=TRUE, rank=TRUE, father=TRUE, pred=TRUE,
succ=TRUE, dist=TRUE)

## How to use a callback
f <- function(graph, data, extra) {
print(data)
FALSE
}
tmp <- bfs(make_ring(10) %du% make_ring(10), root=1, "out",
callback=f)

## How to use a callback to stop the search
## We stop after visiting all vertices in the initial component
f <- function(graph, data, extra) {
data['succ'] == -1
}
bfs(make_ring(10) %du% make_ring(10), root=1, callback=f)



[Package igraph version 1.2.4 Index]