which_multiple: Find the multiple or loop edges in a graph

In igraph: Network Analysis and Visualization

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))

any_multiple(graph)

count_multiple(graph, eids = E(graph))

which_loop(graph, eids = E(graph))

any_loop(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. I.e. 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.

Related documentation in the C library

igraph_is_multiple(), igraph_has_multiple(), igraph_count_multiple(), igraph_is_loop(), igraph_has_loop().

Author(s)

Gabor Csardi [e-mail]

See Also

simplify() to eliminate loop and multiple edges.

Other structural.properties: bfs(), component_distribution(), connect(), constraint(), coreness(), degree(), dfs(), distance_table(), edge_density(), feedback_arc_set(), girth(), is_acyclic(), is_dag(), is_matching(), k_shortest_paths(), knn(), reciprocity(), subcomponent(), subgraph(), topo_sort(), transitivity(), unfold_tree(), which_mutual()

Examples

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

# Multiple edges
g <- sample_pa(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(make_graph(c(1, 2, 2, 1)))
which_multiple(make_graph(c(1, 2, 2, 1), dir = FALSE))

# Remove multiple edges but keep multiplicity
g <- sample_pa(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

igraph documentation built on Oct. 20, 2024, 1:06 a.m.