# R igraph manual pages

Use this if you are using igraph from R

## Convert between directed and undirected graphs

### Description

as.directed converts an undirected graph to directed, as.undirected does the opposite, it converts a directed graph to undirected.

### Usage

as.directed(graph, mode = c("mutual", "arbitrary"))

as.undirected(graph, mode = c("collapse", "each", "mutual"),
edge.attr.comb = igraph_opt("edge.attr.comb"))

### Arguments

 graph The graph to convert. mode Character constant, defines the conversion algorithm. For as.directed it can be mutual or arbitrary. For as.undirected it can be each, collapse or mutual. See details below. edge.attr.comb Specifies what to do with edge attributes, if mode="collapse" or mode="mutual". In these cases many edges might be mapped to a single one in the new graph, and their attributes are combined. Please see attribute.combination for details on this.

### Details

Conversion algorithms for as.directed:

"arbitrary"

The number of edges in the graph stays the same, an arbitrarily directed edge is created for each undirected edge.

"mutual"

Two directed edges are created for each undirected edge, one in each direction.

Conversion algorithms for as.undirected:

"each"

The number of edges remains constant, an undirected edge is created for each directed one, this version might create graphs with multiple edges.

"collapse"

One undirected edge will be created for each pair of vertices which are connected with at least one directed edge, no multiple edges will be created.

"mutual"

One undirected edge will be created for each pair of mutual edges. Non-mutual edges are ignored. This mode might create multiple edges if there are more than one mutual edge pairs between the same pair of vertices.

### Value

A new graph object.

### Author(s)

Gabor Csardi csardi.gabor@gmail.com

simplify for removing multiple and/or loop edges from a graph.

### Examples

g <- make_ring(10)
as.directed(g, "mutual")
g2 <- make_star(10)
as.undirected(g)

# Combining edge attributes
g3 <- make_ring(10, directed=TRUE, mutual=TRUE)
E(g3)$weight <- seq_len(ecount(g3)) ug3 <- as.undirected(g3) print(ug3, e=TRUE) ## Not run: x11(width=10, height=5) layout(rbind(1:2)) plot( g3, layout=layout_in_circle, edge.label=E(g3)$weight)
plot(ug3, layout=layout_in_circle, edge.label=E(ug3)$weight) ## End(Not run) g4 <- graph(c(1,2, 3,2,3,4,3,4, 5,4,5,4, 6,7, 7,6,7,8,7,8, 8,7,8,9,8,9, 9,8,9,8,9,9, 10,10,10,10)) E(g4)$weight <- seq_len(ecount(g4))
ug4 <- as.undirected(g4, mode="mutual",
edge.attr.comb=list(weight=length))
print(ug4, e=TRUE)

[Package igraph version 1.2.3 Index]