What is the feature or improvement you would like to see?

There should be a function that retrieves an edge list in a form suitable for make_graph(), as well as suitable for the C function igraph_create().

as_edgelist() returns a matrix, not a vector, and converting to a vector gives the vertex IDs in the wrong order:

> g<-make_graph(c(1,2, 2,3, 3,4, 4,5))
> as.vector(as_edgelist(g, names=F))
[1] 1 2 3 4 2 3 4 5

Instead one must transpose the matrix first, which is inefficient:

> as.vector(t(as_edgelist(g, names=F)))
[1] 1 2 2 3 3 4 4 5

A more efficient way is

> .Call(igraph:::R_igraph_get_edgelist, g, F)
[1] 0 1 1 2 2 3 3 4

but this uses an internal function.

Use cases for the feature

For libraries that need to convert igraph graphs efficiently, such as leidenbase or leidenalg.

References

• Test failures with the development version of igraph cole-trapnell-lab/leidenbase#39
• Test failures with the development version of igraph kharchenkolab/leidenAlg#13