func (g *Graph) DiscardLowFrequencyNodePtrs(nodeCutoff int64) NodePtrSet {
	cutNodes := getNodesAboveCumCutoff(g.Nodes, nodeCutoff)
	kept := make(NodePtrSet, len(cutNodes))
	for _, n := range cutNodes {
		kept[n] = true
	}
	return kept
}

func makeNodeSet(nodes Nodes, nodeCutoff int64) NodeSet {
	cutNodes := getNodesAboveCumCutoff(nodes, nodeCutoff)
	kept := make(NodeSet, len(cutNodes))
	for _, n := range cutNodes {