get.edge.ids: Find the edge ids based on the incident vertices of the edges
Description
Find the edges in an igraph graph that have the specified end
points. This function handles multi-graph (graphs with multiple edges)
and can consider or ignore the edge directions in directed graphs.
The indicent vertices, given as vertex ids or symbolic
vertex names. They are interpreted pairwise, i.e. the first and
second are used for the first edge, the third and fourth for the
second, etc.
directed
Logical scalar, whether to consider edge directions in
directed graphs. This argument is ignored for undirected graphs.
error
Logical scalar, whether to report an error if an edge is
not found in the graph. If FALSE, then no error is reported,
and zero is returned for the non-existant edge(s).
multi
Logical scalar, whether to handle multiple edges
properly. If FALSE, and a pair of vertices are given twice
(or more), then always the same edge id is reported back for
them. If TRUE, then the edge ids of multiple edg
Value
A numeric vector of edge ids, one for each pair of input
vertices. If there is no edge in the input graph for a given pair of
vertices, then zero is reported. (If the error argument is
FALSE.)
Details
igraph vertex ids are natural numbers, starting from one, up to the
number of vertices in the graph. Similarly, edges are also numbered
from one, up to the number of edges.
This function allows finding the edges of the graph, via their
incident vertices.