Simple graphs are graphs which do not contain loop and multiple edges.

## Usage

simplify(
graph,
remove.multiple = TRUE,
remove.loops = TRUE,
edge.attr.comb = igraph_opt("edge.attr.comb")
)

is_simple(graph)

simplify_and_colorize(graph)

## Arguments

graph

The graph to work on.

remove.multiple

Logical, whether the multiple edges are to be removed.

remove.loops

Logical, whether the loop edges are to be removed.

edge.attr.comb

Specifies what to do with edge attributes, if remove.multiple=TRUE. In this case 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.

## Value

a new graph object with the edges deleted.

## Details

A loop edge is an edge for which the two endpoints are the same vertex. Two edges are multiple edges if they have exactly the same two endpoints (for directed graphs order does matter). A graph is simple is it does not contain loop edges and multiple edges.

is_simple() checks whether a graph is simple.

simplify() removes the loop and/or multiple edges from a graph. If both remove.loops and remove.multiple are TRUE the function returns a simple graph.

simplify_and_colorize() constructs a new, simple graph from a graph and also sets a color attribute on both the vertices and the edges. The colors of the vertices represent the number of self-loops that were originally incident on them, while the colors of the edges represent the multiplicities of the same edges in the original graph. This allows one to take into account the edge multiplicities and the number of loop edges in the VF2 isomorphism algorithm. Other graph, vertex and edge attributes from the original graph are discarded as the primary purpose of this function is to facilitate the usage of multigraphs with the VF2 algorithm.

which_loop(), which_multiple() and count_multiple(), delete_edges(), delete_vertices()

Other functions for manipulating graph structure: +.igraph(), add_edges(), add_vertices(), complementer(), compose(), connect(), contract(), delete_edges(), delete_vertices(), difference.igraph(), difference(), disjoint_union(), edge(), igraph-minus, intersection.igraph(), intersection(), path(), permute(), rep.igraph(), reverse_edges(), union.igraph(), union(), vertex()

Other functions for manipulating graph structure: +.igraph(), add_edges(), add_vertices(), complementer(), compose(), connect(), contract(), delete_edges(), delete_vertices(), difference.igraph(), difference(), disjoint_union(), edge(), igraph-minus, intersection.igraph(), intersection(), path(), permute(), rep.igraph(), reverse_edges(), union.igraph(), union(), vertex()

Other functions for manipulating graph structure: +.igraph(), add_edges(), add_vertices(), complementer(), compose(), connect(), contract(), delete_edges(), delete_vertices(), difference.igraph(), difference(), disjoint_union(), edge(), igraph-minus, intersection.igraph(), intersection(), path(), permute(), rep.igraph(), reverse_edges(), union.igraph(), union(), vertex()

## Author

Gabor Csardi csardi.gabor@gmail.com

## Examples


g <- make_graph(c(1, 2, 1, 2, 3, 3))
is_simple(g)
#>  FALSE
is_simple(simplify(g, remove.loops = FALSE))
#>  FALSE
is_simple(simplify(g, remove.multiple = FALSE))
#>  FALSE
is_simple(simplify(g))
#>  TRUE