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package uk.ac.ox.cs.data.sample;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Random;
import java.util.Set;
import java.util.Stack;
import org.openrdf.rio.RDFHandlerException;
import org.openrdf.rio.turtle.TurtleWriter;
import uk.ac.ox.cs.pagoda.util.Utility;
public class RandomWalk extends Sampler {
public RandomWalk(RDFGraph graph, TurtleWriter writer) {
super(graph, writer);
}
protected Random rand = new Random();
protected int noOfStatements = 0, statementLimit = 0;
protected Set<Integer> visited = new HashSet<Integer>();
@Override
public void setLimit(int limit) {
statementLimit = limit;
}
@Override
public void sample() throws RDFHandlerException {
int u, v, pick, index;
RDFEdge edge;
List<RDFEdge> edges;
Stack<Integer> stack = new Stack<Integer>();
while (true) {
if (noOfStatements >= statementLimit) {
return ;
}
if (stack.isEmpty()) {
stack.add(v = rand.nextInt(m_graph.numberOfIndividuals));
Utility.logInfo("A new start: " + m_graph.getRawString(v));
visit(v);
}
u = stack.peek();
if (rand.nextInt(100) < 15) {
stack.pop();
continue;
}
if ((edges = m_graph.edges.get(u)) == null || edges.size() == 0) {
stack.clear();
continue;
}
index = 0;
pick = rand.nextInt(edges.size());
for (Iterator<RDFEdge> iter = edges.iterator(); iter.hasNext(); ++index) {
edge = iter.next();
if (index == pick) {
stack.add(v = edge.m_dst);
visit(v);
m_writer.handleStatement(m_graph.getStatement(u, edge.m_label, edge.m_dst));
++noOfStatements;
iter.remove();
}
}
}
}
protected void visit(int node) throws RDFHandlerException {
if (visited.contains(node)) return ;
visited.add(node);
List<Integer> list = m_graph.labels.get(node);
if (list == null) return ;
for (Iterator<Integer> iter = list.iterator(); iter.hasNext(); )
m_writer.handleStatement(m_graph.getStatement(node, iter.next()));
noOfStatements += list.size();
}
@Override
public void dispose() {
visited.clear();
}
}
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