# R igraph manual pages

Use this if you are using igraph from R

 which_multiple {igraph} R Documentation

## Find the multiple or loop edges in a graph

### Description

A loop edge is an edge from a vertex to itself. An edge is a multiple edge if it has exactly the same head and tail vertices as another edge. A graph without multiple and loop edges is called a simple graph.

### Usage

which_multiple(graph, eids = E(graph))


### Arguments

 graph The input graph. eids The edges to which the query is restricted. By default this is all edges in the graph.

### Details

any_loop decides whether the graph has any loop edges.

which_loop decides whether the edges of the graph are loop edges.

any_multiple decides whether the graph has any multiple edges.

which_multiple decides whether the edges of the graph are multiple edges.

count_multiple counts the multiplicity of each edge of a graph.

Note that the semantics for which_multiple and count_multiple is different. which_multiple gives TRUE for all occurrences of a multiple edge except for one. Ie. if there are three i-j edges in the graph then which_multiple returns TRUE for only two of them while count_multiple returns ‘3’ for all three.

See the examples for getting rid of multiple edges while keeping their original multiplicity as an edge attribute.

### Value

any_loop and any_multiple return a logical scalar. which_loop and which_multiple return a logical vector. count_multiple returns a numeric vector.

### Author(s)

Gabor Csardi csardi.gabor@gmail.com

simplify to eliminate loop and multiple edges.

### Examples


# Loops
g <- graph( c(1,1,2,2,3,3,4,5) )
any_loop(g)
which_loop(g)

# Multiple edges
g <- barabasi.game(10, m=3, algorithm="bag")
any_multiple(g)
which_multiple(g)
count_multiple(g)
which_multiple(simplify(g))
all(count_multiple(simplify(g)) == 1)

# Direction of the edge is important
which_multiple(graph( c(1,2, 2,1) ))
which_multiple(graph( c(1,2, 2,1), dir=FALSE ))

# Remove multiple edges but keep multiplicity
g <- barabasi.game(10, m=3, algorithm="bag")
E(g)$weight <- count_multiple(g) g <- simplify(g, edge.attr.comb=list(weight = "min")) any(which_multiple(g)) E(g)$weight



[Package igraph version 1.3.5 Index]