Supports for graph metric computations on node subset not all nodes in a graph

[mgao97]

I think this is a common problem for several graph metrics and could be easily supported.

Take node degree as an example. Suppose we have a graph with 100k nodes and 500k edges. I just want to know the degree values of 100 nodes within that graph.

One direct way is to just compute the degree values of these 100 nodes. Existing implementations seem to require computing all the nodes and then selecting the values corresponding to the desired nodes.