R: Conversions "graph" <-> (sparse) Matrix

coerce-methods-graph {Matrix}

R Documentation

Conversions "graph" <–> (sparse) Matrix

Description

Since 2005, package Matrix has supported coercions to and from class graph from package graph. Since 2013, this functionality has been exposed via functions T2graph and graph2T, which, unlike methods for as(from, "<Class>"), support optional arguments.

Usage

graph2T(from, use.weights = )
T2graph(from, need.uniq = !isUniqueT(from), edgemode = NULL)

Arguments

`from`	for `graph2T()`, an R object of class `"graph"`; for `T2graph()`, a sparse matrix inheriting from `"TsparseMatrix"`.
`use.weights`	logical indicating if weights should be used, i.e., equivalently the result will be numeric, i.e. of class `dgTMatrix`; otherwise the result will be `ngTMatrix` or `nsTMatrix`, the latter if the graph is undirected. The default looks if there are weights in the graph, and if any differ from `1`, weights are used.
`need.uniq`	a logical indicating if `from` may need to be internally “uniqified”; do not set this and hence rather use the default, unless you know what you are doing!
`edgemode`	one of `NULL`, `"directed"`, or `"undirected"`. The default `NULL` looks if the matrix is symmetric and assumes `"undirected"` in that case.

Value

For graph2T(), a sparse matrix inheriting from "TsparseMatrix".

For T2graph() an R object of class "graph".

Examples

if(requireNamespace("graph")) {
  n4 <- LETTERS[1:4]; dns <- list(n4,n4)
  show(a1 <- sparseMatrix(i= c(1:4),   j=c(2:4,1),   x = 2,    dimnames=dns))
  show(g1 <- as(a1, "graph")) # directed
  unlist(graph::edgeWeights(g1)) # all '2'

  show(a2 <- sparseMatrix(i= c(1:4,4), j=c(2:4,1:2), x = TRUE, dimnames=dns))
  show(g2 <- as(a2, "graph")) # directed
  # now if you want it undirected:
  show(g3  <- T2graph(as(a2,"TsparseMatrix"), edgemode="undirected"))
  show(m3 <- as(g3,"Matrix"))
  show( graph2T(g3) ) # a "pattern Matrix" (nsTMatrix)

  a. <- sparseMatrix(i=4:1, j=1:4, dimnames=list(n4, n4), repr="T") # no 'x'
  show(a.) # "ngTMatrix"
  show(g. <- as(a., "graph"))

}