igraph (version 0.5.2-2)

is.multiple: 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

is.loop(graph, eids=E(graph))
is.multiple(graph, eids=E(graph))
count.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.

Value

  • is.loop and is.multiple return a logical vector. count.multiple returns a numeric vector.

concept

Simple graph

Details

Note that the semantics for is.multiple and count.multiple is different. is.multiple gives TRUE for all occurences of a multiple edge except for one. Ie. if there are three i-j edges in the graph then is.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.

See Also

simplify to eliminate loop and multiple edges.

Examples

Run this code
# Loops
g <- graph( c(0,0,1,1,2,2,3,4) )
is.loop(g)

# Multiple edges
g <- barabasi.game(10, m=3)
is.multiple(g)
count.multiple(g)
is.multiple(simplify(g))
all(count.multiple(simplify(g)) == 1)

# Direction of the edge is important
is.multiple(graph( c(0,1, 1,0) ))
is.multiple(graph( c(0,1, 1,0), dir=FALSE ))

# Remove multiple edges but keep multiplicity
g <- barabasi.game(10, m=3)
E(g)$weight <- count.multiple(g)
g <- simplify(g)
any(is.multiple(g))
E(g)$weight

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