/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.flink.graph.generator;
import org.apache.flink.api.common.functions.FlatMapFunction;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.ExecutionEnvironment;
import org.apache.flink.api.java.functions.FunctionAnnotation.ForwardedFields;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.graph.Edge;
import org.apache.flink.graph.Graph;
import org.apache.flink.graph.Vertex;
import org.apache.flink.types.LongValue;
import org.apache.flink.types.NullValue;
import org.apache.flink.util.Collector;
import org.apache.flink.util.LongValueSequenceIterator;
import org.apache.flink.util.Preconditions;
import java.util.ArrayList;
import java.util.List;
/**
* @see <a href="http://mathworld.wolfram.com/GridGraph.html">Grid Graph at Wolfram MathWorld</a>
*/
public class GridGraph
extends AbstractGraphGenerator<LongValue, NullValue, NullValue> {
// Required to create the DataSource
private final ExecutionEnvironment env;
// Required configuration
private List<Tuple2<Long, Boolean>> dimensions = new ArrayList<>();
private long vertexCount = 1;
/**
* An undirected {@code Graph} connecting vertices in a regular tiling in
* one or more dimensions and where the endpoints are optionally connected.
*
* @param env the Flink execution environment
*/
public GridGraph(ExecutionEnvironment env) {
this.env = env;
}
/**
* Required configuration for each dimension of the graph.
*
* @param size number of vertices; dimensions of size 1 are prohibited due to having no effect
* on the generated graph
* @param wrapEndpoints whether to connect first and last vertices; this has no effect on
* dimensions of size 2
* @return this
*/
public GridGraph addDimension(long size, boolean wrapEndpoints) {
Preconditions.checkArgument(size >= 2, "Dimension size must be at least 2");
vertexCount *= size;
// prevent duplicate edges
if (size == 2) {
wrapEndpoints = false;
}
dimensions.add(new Tuple2<>(size, wrapEndpoints));
return this;
}
@Override
public Graph<LongValue, NullValue, NullValue> generate() {
Preconditions.checkState(!dimensions.isEmpty(), "No dimensions added to GridGraph");
// Vertices
DataSet<Vertex<LongValue, NullValue>> vertices = GraphGeneratorUtils.vertexSequence(env, parallelism, vertexCount);
// Edges
LongValueSequenceIterator iterator = new LongValueSequenceIterator(0, this.vertexCount - 1);
DataSet<Edge<LongValue, NullValue>> edges = env
.fromParallelCollection(iterator, LongValue.class)
.setParallelism(parallelism)
.name("Edge iterators")
.flatMap(new LinkVertexToNeighbors(vertexCount, dimensions))
.setParallelism(parallelism)
.name("Grid graph edges");
// Graph
return Graph.fromDataSet(vertices, edges, env);
}
@ForwardedFields("*->f0")
private static class LinkVertexToNeighbors
implements FlatMapFunction<LongValue, Edge<LongValue, NullValue>> {
private long vertexCount;
private List<Tuple2<Long, Boolean>> dimensions;
private LongValue target = new LongValue();
private Edge<LongValue, NullValue> edge = new Edge<>(null, target, NullValue.getInstance());
public LinkVertexToNeighbors(long vertexCount, List<Tuple2<Long, Boolean>> dimensions) {
this.vertexCount = vertexCount;
this.dimensions = dimensions;
}
@Override
public void flatMap(LongValue source, Collector<Edge<LongValue, NullValue>> out)
throws Exception {
edge.f0 = source;
long val = source.getValue();
// the distance between neighbors in a given iteration
long increment = vertexCount;
// the value in the remaining dimensions
long remainder = val;
for (Tuple2<Long, Boolean> dimension : dimensions) {
increment /= dimension.f0;
// the index within this dimension
long index = remainder / increment;
if (index > 0) {
target.setValue(val - increment);
out.collect(edge);
} else if (dimension.f1) {
target.setValue(val + increment * (dimension.f0 - 1));
out.collect(edge);
}
if (index < dimension.f0 - 1) {
target.setValue(val + increment);
out.collect(edge);
} else if (dimension.f1) {
target.setValue(val - increment * (dimension.f0 - 1));
out.collect(edge);
}
remainder %= increment;
}
}
}
}