CODEWITHSUNDEEP
rigraph
Nick
Nick

Reputation: 1116

How to union graphs and save directed and undirected components in new graph?

I have read the can-an-igraph-object-have-directed-and-undirected-edges.

I have two graphs gUed and gDed.

The gUed is the undirected graph and the gDed is the directed one. I need to union these graph into one. I made this union with the edge list.

library(igraph)
gDed <- graph.formula(1-+2, 2-+3, 3-+4, 4-+5)

gUed <- graph.formula(6--1, 7--2, 8--4, 9--5)

EL  = as_edgelist(gDed, names = TRUE)
EL1 = as_edgelist(gUed, names = TRUE)
ELU = rbind(EL, EL1)
ELU = ELU[!duplicated(ELU),]
GU = graph_from_edgelist(ELU)

## To check the result
par(mfrow=c(1,3))
plot(gDed)
plot(gUed)
plot(GU)

enter image description here

But I have a problem: in new graph GU all edges are directed.

Question. How to union two graphs and save directed and undirected components in new graph?

Upvotes: 0

Views: 131

Answers (1)

desval
desval

Reputation: 2435

A network has to be either directed or undirected. That said, you can work around that, a bit.

Similar to the answer you found, you create a directed network, and pass in an argument that keeps track of whether the edge is directed or not. You can use this when you plot, or to subset your network:

E(gDed)$type <- "dir"
E(gUed)$type <- "undir"


g <- graph_from_data_frame(
  rbind(
    as_data_frame(gDed, what = "edges"),
    as_data_frame(gUed, what = "edges")
  )
)


plot(g,
     edge.arrow.mode = ifelse(E(g)$type=="undir", "-", ">"))


g_sub1 <- subgraph.edges(g, eids = E(g)[E(g)$type=="undir"] )
plot(g_sub1,
     edge.arrow.mode = ifelse(E(g_sub1)$type=="undir", "-", ">"))


g_sub2 <- subgraph.edges(g, eids = E(g)[E(g)$type!="undir"] )
plot(g_sub2,
     edge.arrow.mode = ifelse(E(g_sub2)$type=="undir", "-", ">"))

If there are double edges, one directed and one undirected, they will both be in g, leading to weird plots. You could fix this by creating a third type of edge, which will be either directed or undirected, depending on what you want to do.

Upvotes: 1

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