Question about how to get dfs() working ?

Usage
,
1

E.g. I wonder if it is possible to compute the “layer” of all vertices of a directed tree using igraph::dfs(). Without using other functions that implicitly traverse the graph such as shortst_paths(), distances(), degree(), layout_with_sugiyama().

The layer of a vertex is (recursively) defined as

  • equal to zero if there are no outgoing edges and
  • otherwise the largest layer among the successors, plus 1.

It is straightforward to code this manually, but the native dfs() is obviously much faster.

2

Thanks. ?dfs has an example for the out.callback argument, is that helpful?

3

You seem to be asking to compute the Strahler stream order. While this is very straightforward when programming igraph in C, I failed when I tried to do it in R a while ago.

@krlmlr, I suggest you try to do this before settling on a solution for the above issue.

Basically you need to iterate through vertices according to order.out, then whenever the parent p of a vertex v doesn’t have a higher stream order, set its stream order of p to that of the v plus one.

Note that it is not necessary to use the callback function.