Use this if you are using igraph from R
dfs {igraph}  R Documentation 
Depthfirst search is an algorithm to traverse a graph. It starts from a root vertex and tries to go quickly as far from as possible.
dfs(
graph,
root,
mode = c("out", "in", "all", "total"),
unreachable = TRUE,
order = TRUE,
order.out = FALSE,
father = FALSE,
dist = FALSE,
in.callback = NULL,
out.callback = NULL,
extra = NULL,
rho = parent.frame(),
neimode
)
graph 
The input graph. 
root 
The single root vertex to start the search from. 
mode 
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

order 
Logical scalar, whether to return the DFS ordering of the vertices. 
order.out 
Logical scalar, whether to return the ordering based on leaving the subtree of the vertex. 
father 
Logical scalar, whether to return the father of the vertices. 
dist 
Logical scalar, whether to return the distance from the root of the search tree. 
in.callback 
If not 
out.callback 
If not 
extra 
Additional argument to supply to the callback function. 
rho 
The environment in which the callback function is evaluated. 
neimode 
This argument is deprecated from igraph 1.3.0; use

The callback functions must have the following arguments:
The input graph is passed to the callback function here.
A named numeric vector, with the following entries: ‘vid’, the vertex that was just visited and ‘dist’, its distance from the root of the search tree.
The extra argument.
The callback must return FALSE to continue the search or TRUE to terminate it. See examples below on how to use the callback functions.
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 
order 
Numeric vector. The vertex ids, in the order in which they were visited by the search. 
order.out 
Numeric vector, the vertex ids, in the order of the completion of their subtree. 
father 
Numeric vector. The father of each vertex, i.e. the vertex it was discovered from. 
dist 
Numeric vector, for each vertex its distance from the root of the search tree. 
Note that order
, order.out
, father
, and dist
might be NULL
if their corresponding argument is FALSE
, i.e.
if their calculation is not requested.
Gabor Csardi csardi.gabor@gmail.com
bfs
for breadthfirst search.
## A graph with two separate trees
dfs(make_tree(10) %du% make_tree(10), root=1, "out",
TRUE, TRUE, TRUE, TRUE)
## How to use a callback
f.in < function(graph, data, extra) {
cat("in:", paste(collapse=", ", data), "\n")
FALSE
}
f.out < function(graph, data, extra) {
cat("out:", paste(collapse=", ", data), "\n")
FALSE
}
tmp < dfs(make_tree(10), root=1, "out",
in.callback=f.in, out.callback=f.out)
## Terminate after the first component, using a callback
f.out < function(graph, data, extra) {
data['vid'] == 1
}
tmp < dfs(make_tree(10) %du% make_tree(10), root=1,
out.callback=f.out)