Avoid warning logs: Don't add edges between excluded nodes to graph copy

Author: flowtoolz

Code/Graph+Copying.swift

@@ -32,6 +32,9 @@ extension Graph
 
         for originalEdge in includedEdges ?? Set(edgesByID.values)
         {
+            guard graphCopy.contains(originalEdge.source.id),
+                  graphCopy.contains(originalEdge.target.id) else { continue }
+            
             graphCopy.addEdge(from: originalEdge.source.id,
                               to: originalEdge.target.id,
                               count: originalEdge.count)

Code/Graph/Graph.swift

@@ -145,6 +145,11 @@ public class Graph<NodeID: Hashable, NodeValue>
         nodesByID.values.filter { $0.isSink }
     }
 
+    public func contains(_ nodeID: NodeID) -> Bool
+    {
+        node(for: nodeID) != nil
+    }
+    
     public func contains(_ node: Node) -> Bool
     {
         self.node(for: node.id) === node