as_adj_list
returns a list of numeric vectors, which include the ids
of neighbor vertices (according to the mode
argument) of all
vertices.
as_adj_edge_list
returns a list of numeric vectors, which include the
ids of adjacent edgs (according to the mode
argument) of all
vertices.
If igraph_opt("return.vs.es")
is true (default), the numeric
vectors of the adjacency lists are coerced to igraph.vs
, this can be
a very expensive operation on large graphs.