Graph.successors(): add support for ordering the nodes

Graph.successors() returns nodes in an undetermined order which makes it difficult to use Graph as a rooted tree where the ordering of the children is important (e.g. something similar to XML) with a schema that orders some elements).

I have the following workaround but it seems expensive (although for small trees I suppose it doesn’t really matter):

fun <N> Graph<N>.children(node: N): Set<N> {
    return nodes().toMutableSet().apply { retainAll(successors(node)) }
}

Can supported be added to specify the order of nodes returned by successors()?

[nymanjens]

Hi, I’m a also a maintainer of this library and just added the possibility of returning successors in insertion order. This should be included in the next Guava release for Graph and ValueGraph. Network support comes later.

Example of how to enable this:

GraphBuilder.directed().incidentEdgeOrder(ElementOrder.stable()).build()

This gives the following guarantees:

• edges(): Stable order
• adjacentNodes(node): Connecting edge insertion order
• predecessors(node): Connecting edge insertion order
• successors(node): Connecting edge insertion order
• incidentEdges(node): Edge insertion order

[nymanjens]

Fair enough, that sounds like a use case that would indeed benefit from a similar feature on Network