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Spark algorithms for building k-nn graphs

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package info.debatty.spark.knngraphs.example;

import info.debatty.java.graphs.NeighborList;
import info.debatty.java.graphs.Node;
import info.debatty.java.utils.SparseIntegerVector;
import info.debatty.spark.knngraphs.builder.LSHSuperBitSparseIntegerVector;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaPairRDD;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.JavaSparkContext;

/**
 * An example of how to use LSHSuperBit algorithm to build a k-nn graph from
 * a dataset of SparseIntegerVector
 * 
 * @author Thibault Debatty
 */
public class LSHSuperBitSparseIntegerVectorExample {

    /**
     * @param args the command line arguments
     * @throws java.lang.Exception
     */
    public static void main(String[] args) throws Exception {
        
        // Configure spark instance
        SparkConf conf = new SparkConf();
        conf.setAppName("SparkTest");
        conf.setIfMissing("spark.master", "local[*]");
        JavaSparkContext sc = new JavaSparkContext(conf);
        
        // Create some nodes consisting of SparseIntegerVector
        int d = 1000; // dimensions
        int n = 1000; // items
        Random r = new Random();
        List> data = 
                new ArrayList>();
        for (int i = 0; i < n; i++) {
            int[] vector = new int[d];
            for (int j = 0; j < d/2; j++) {
                vector[r.nextInt(d)] = r.nextInt(100);
            }
            
            data.add(new Node(
                    String.valueOf(i), 
                    new SparseIntegerVector(vector)));
        }
        JavaRDD> nodes = sc.parallelize(data);
        
        
        // Configure LSHSuperBit graph builder
        LSHSuperBitSparseIntegerVector gbuilder =
                new LSHSuperBitSparseIntegerVector();
        gbuilder.setK(10);
        gbuilder.setStages(2);
        gbuilder.setBuckets(10);
        // LSH hashing requires the dimensionality
        gbuilder.setDim(d);
        
        // By default, LSHSuperBit graph builder uses cosine similarity
        // but another similarity measure can be defined if needed...
        
        // Build the graph...
        JavaPairRDD, NeighborList> graph = 
                gbuilder.computeGraph(nodes);
        System.out.println(graph.first());
    }
}