Topological sort of vertices in directed acyclic graph

A topological ordering of a directed graph is a linear ordering of its vertices such that, for every edge (u->v), u comes before v in the ordering. A topological ordering is possible if and only if the graph has no directed cycles, that is, if it is a directed acyclic graph (DAG). Any DAG has at least one topological ordering. Can hence be used for checking if a graph is a DAG.

topo_sort(object, index = FALSE)

topo_sortMAT(amat, index = FALSE)

topoSort(object, index = FALSE)

topoSortMAT(amat, index = FALSE)

Arguments

object: An graph represented either as a graphNEL object, an igraph, a (dense) matrix, a (sparse) dgCMatrix.
index: If FALSE, an ordering is returned if it exists and character(0) otherwise. If TRUE, the index of the variables in an adjacency matrix is returned and -1 otherwise.
amat: Adjacency matrix.

Value

If FALSE, an ordering is returned if it exists and character(0) otherwise. If TRUE, the index of the variables in an adjacency matrix is returned and -1 otherwise.

Note

The workhorse is the topo_sortMAT function which takes an adjacency matrix as input.

Synonymous functions

The functions topo_sort / topoSort are synonymous with topo_sortMAT / topoSortMAT. One of the groups may be deprecated in the future.

Author

Søren Højsgaard, sorenh@math.aau.dk

Examples

dagMAT  <- dag(~a:b:c + c:d:e, result="matrix")
dagMATS <- as(dagMAT, "dgCMatrix")

topo_sort(dagMAT)
#> Error in ensure_igraph(graph): Must provide a graph object (provided wrong object type).
topo_sort(dagMATS)
#> Error in ensure_igraph(graph): Must provide a graph object (provided wrong object type).