Builds a subgraph of a graph for a set of nodes.
Usage:
// Let's say you have a `srcGraph` with two edges:
// digraph srcGraph {
// a -> b;
// b -> c;
// }
var getSubgraph = require('ngraph.subgraph');
var g1 = getSubgraph(new Set(['a', 'b']), srcGraph);
// Now g1 has both `a` and `b`, and edge between them:
// digraph g1 {
// a -> b
// }
// If you pass just 'a', and 'c' - no edge will be present in g2:
var g2 = getSubgraph(new Set(['a', 'c'], srcGraph);
// digraph g2 {
// a;
// c;
// }MIT