@Override
public IVertexSequence<V> next() {
if (!hasNext()) throw new NoSuchElementException();
// Generate a random walk starting at vertex order[current]
int currVertexIdx = order[position++];
int[] indices = new int[walkLength + 1];
indices[0] = currVertexIdx;
if (walkLength == 0) return new VertexSequence<>(graph, indices);
Vertex<V> next;
try {
next = graph.getRandomConnectedVertex(currVertexIdx, rng);
} catch (NoEdgesException e) {
switch (mode) {
case SELF_LOOP_ON_DISCONNECTED:
for (int i = 1; i < walkLength; i++) indices[i] = currVertexIdx;
return new VertexSequence<>(graph, indices);
case EXCEPTION_ON_DISCONNECTED:
throw e;
default:
throw new RuntimeException("Unknown/not implemented NoEdgeHandling mode: " + mode);
}
}
indices[1] = next.vertexID();
currVertexIdx = indices[1];
for (int i = 2;
i <= walkLength;
i++) { // <= walk length: i.e., if walk length = 2, it contains 3 vertices etc
next = graph.getRandomConnectedVertex(currVertexIdx, rng);
currVertexIdx = next.vertexID();
indices[i] = currVertexIdx;
}
return new VertexSequence<>(graph, indices);
}
@Override
public IVertexSequence<V> next() {
if (!hasNext()) throw new NoSuchElementException();
// Generate a weighted random walk starting at vertex order[current]
int currVertexIdx = order[position++];
int[] indices = new int[walkLength + 1];
indices[0] = currVertexIdx;
if (walkLength == 0) return new VertexSequence<>(graph, indices);
for (int i = 1; i <= walkLength; i++) {
List<? extends Edge<? extends Number>> edgeList = graph.getEdgesOut(currVertexIdx);
// First: check if there are any outgoing edges from this vertex. If not: handle the situation
if (edgeList == null || edgeList.size() == 0) {
switch (mode) {
case SELF_LOOP_ON_DISCONNECTED:
for (int j = i; j < walkLength; j++) indices[j] = currVertexIdx;
return new VertexSequence<>(graph, indices);
case EXCEPTION_ON_DISCONNECTED:
throw new NoEdgesException(
"Cannot conduct random walk: vertex "
+ currVertexIdx
+ " has no outgoing edges. "
+ " Set NoEdgeHandling mode to NoEdgeHandlingMode.SELF_LOOP_ON_DISCONNECTED to self loop instead of "
+ "throwing an exception in this situation.");
default:
throw new RuntimeException("Unknown/not implemented NoEdgeHandling mode: " + mode);
}
}
// To do a weighted random walk: we need to know total weight of all outgoing edges
double totalWeight = 0.0;
for (Edge<? extends Number> edge : edgeList) {
totalWeight += edge.getValue().doubleValue();
}
double d = rng.nextDouble();
double threshold = d * totalWeight;
double sumWeight = 0.0;
for (Edge<? extends Number> edge : edgeList) {
sumWeight += edge.getValue().doubleValue();
if (sumWeight >= threshold) {
if (edge.isDirected()) {
currVertexIdx = edge.getTo();
} else {
if (edge.getFrom() == currVertexIdx) {
currVertexIdx = edge.getTo();
} else {
currVertexIdx =
edge
.getFrom(); // Undirected edge: might be next--currVertexIdx instead of
// currVertexIdx--next
}
}
indices[i] = currVertexIdx;
break;
}
}
}
return new VertexSequence<>(graph, indices);
}
/**
* @param graph IGraph to conduct walks on
* @param walkLength length of each walk. Walk of length 0 includes 1 vertex, walk of 1 includes 2
* vertices etc
* @param rngSeed seed for randomization
* @param mode mode for handling random walks from vertices with either no edges, or no outgoing
* edges (for directed graphs)
*/
public WeightedRandomWalkIterator(
IGraph<V, ? extends Number> graph, int walkLength, long rngSeed, NoEdgeHandling mode) {
this(graph, walkLength, rngSeed, mode, 0, graph.numVertices());
}
/**
* @param graph IGraph to conduct walks on
* @param walkLength length of each walk. Walk of length 0 includes 1 vertex, walk of 1 includes 2
* vertices etc
* @param rngSeed seed for randomization
* @param mode mode for handling random walks from vertices with either no edges, or no outgoing
* edges (for directed graphs)
*/
public RandomWalkIterator(IGraph<V, ?> graph, int walkLength, long rngSeed, NoEdgeHandling mode) {
this(graph, walkLength, rngSeed, mode, 0, graph.numVertices());
}