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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.stringsimilarity.KShingling;
import info.debatty.java.utils.SparseIntegerVector;
import info.debatty.spark.knngraphs.builder.DistributedGraphBuilder;
import info.debatty.spark.knngraphs.builder.LSHSuperBitSparseIntegerVector;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
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 text dataset 
 * 
 * @author Thibault Debatty
 */
public class LSHSuperBitTextExample {

    /**
     * @param args the command line arguments
     * @throws java.io.IOException
     */
    public static void main(String[] args) throws IOException, Exception {
        
        if (args.length != 1) {
            System.out.println(
                    "Usage: spark-submit --class " +
                    Search.class.getCanonicalName() + " " +
                    "");
        }
        
        String file =  args[0];
        
        // Read the file
        ArrayList strings = DistributedGraphBuilder.readFile(file);
        
        // Convert the strings to nodes of SparseIntegerVectors
        // using k-shingling
        // we will split strings in 3-grams (sequences of 3 characters)
        KShingling ks = new KShingling(3);
        List> data = 
                new ArrayList>();
        for (int i = 0; i < strings.size(); i++) {
            String s = strings.get(i);
            data.add(new Node(
                    s,                      // id
                    ks.getProfile(s).getSparseVector()));   // value
        }
        
        int dim = ks.getDimension();
        
        // Configure spark instance
        SparkConf conf = new SparkConf();
        conf.setAppName("SparkTest");
        conf.setIfMissing("spark.master", "local[*]");
        JavaSparkContext sc = new JavaSparkContext(conf);
        
        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(dim);
        
        // 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());
    }
}