Efficient way to have unique edges (with given vertices and type)

graph-tool
1

Hi,

I would like to know if there is a computationally efficient way of creating edges only if an edge with the same extremities and the same type (= a given edge property, in the sense of graph-tool edge properties) does not exist already.

Of course I can use the following algorithm:

before creating edge (v1,v2) of type t1:
take all edges out-going from v1:
check how many of them have v2 as target,
among them: check whether one of them has type t1
if yes do not create a new edge and return this one
if not, create a new edge

As this seems to be a bit slow (I have to do many such edge creations) I was wondering if there is a more efficient « create-only-if-doesnt-exist-already » method, of maybe simply a query method including the type (a single method for checking if there exists an edge of a given type between two given vertices).

Thanks in advance

Yannis

2

It is worthwhile to look at the documentation for questions like
this.

What you are looking for is the Graph.edge() function:

      https://graph-tool.skewed.de/static/doc/graph_tool.html#graph_tool.Graph.edge

If you pass "all_edges=True" this will give you a list of all the
existing parallel edges incident on two nodes. You can then iterate
through them and check if one of them has the correct property value. If
not, you create a new edge.

Best,
Tiago