% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/structural.properties.R
\name{bfs}
\alias{bfs}
\alias{graph.bfs}
\title{Breadth-first search}
\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{
\item{graph}{The input graph.}

\item{root}{Numeric vector, usually of length one. The root vertex, or root
vertices to start the search from.}

\item{neimode}{For directed graphs specifies the type of edges to follow.
\sQuote{out} follows outgoing, \sQuote{in} incoming edges. \sQuote{all}
ignores edge directions completely. \sQuote{total} is a synonym for
\sQuote{all}. This argument is ignored for undirected graphs.}

\item{unreachable}{Logical scalar, whether the search should visit the
vertices that are unreachable from the given root vertex (or vertices). If
\code{TRUE}, then additional searches are performed until all vertices are
visited.}

\item{restricted}{\code{NULL} (=no restriction), or a vector of vertices
(ids or symbolic names). In the latter case, the search is restricted to the
given vertices.}

\item{order}{Logical scalar, whether to return the ordering of the vertices.}

\item{rank}{Logical scalar, whether to return the rank of the vertices.}

\item{father}{Logical scalar, whether to return the father of the vertices.}

\item{pred}{Logical scalar, whether to return the predecessors of the
vertices.}

\item{succ}{Logical scalar, whether to return the successors of the
vertices.}

\item{dist}{Logical scalar, whether to return the distance from the root of
the search tree.}

\item{callback}{If not \code{NULL}, then it must be callback function. This
is called whenever a vertex is visited. See details below.}

\item{extra}{Additional argument to supply to the callback function.}

\item{rho}{The environment in which the callback function is evaluated.}
}
\value{
A named list with the following entries: \item{root}{Numeric scalar.
The root vertex that was used as the starting point of the search.}
\item{neimode}{Character scalar. The \code{neimode} argument of the function
call. Note that for undirected graphs this is always \sQuote{all},
irrespectively of the supplied value.} \item{order}{Numeric vector. The
vertex ids, in the order in which they were visited by the search.}
\item{rank}{Numeric vector. The rank for each vertex.} \item{father}{Numeric
vector. The father of each vertex, i.e. the vertex it was discovered from.}
\item{pred}{Numeric vector. The previously visited vertex for each vertex,
or 0 if there was no such vertex.} \item{succ}{Numeric vector. The next
vertex that was visited after the current one, or 0 if there was no such
vertex.} \item{dist}{Numeric vector, for each vertex its distance from the
root of the search tree.}

Note that \code{order}, \code{rank}, \code{father}, \code{pred}, \code{succ}
and \code{dist} might be \code{NULL} if their corresponding argument is
\code{FALSE}, i.e. if their calculation is not requested.
}
\description{
Breadth-first search is an algorithm to traverse a graph. We start from a
root vertex and spread along every edge \dQuote{simultaneously}.
}
\details{
The callback function must have the following arguments: \describe{
\item{graph}{The input graph is passed to the callback function here.}
\item{data}{A named numeric vector, with the following entries:
\sQuote{vid}, the vertex that was just visited, \sQuote{pred}, its
predecessor, \sQuote{succ}, its successor, \sQuote{rank}, the rank of the
current vertex, \sQuote{dist}, its distance from the root of the search
tree.} \item{extra}{The extra argument.} } See examples below on how to use
the callback function.
}
\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)


}
\seealso{
\code{\link{dfs}} for depth-first search.
}
\author{
Gabor Csardi \email{csardi.gabor@gmail.com}
}
\keyword{graphs}
