Java ConcurrentHashMap.merge方法代码示例

import java.util.concurrent.ConcurrentHashMap; //导入方法依赖的package包/类
/**
 * merge removes when the given key is present and function returns null
 */
public void testMerge3() {
    ConcurrentHashMap map = map5();
    map.merge(one, "Y", (x, y) -> null);
    assertFalse(map.containsKey(one));
}
 

import java.util.concurrent.ConcurrentHashMap; //导入方法依赖的package包/类
/** Initialize cluster centers. */
private Vector[] initClusterCenters(SparseDistributedMatrix points, int k) {
    // Initialize empty centers and point costs.
    int ptsCnt = points.rowSize();

    String cacheName = ((SparseDistributedMatrixStorage)points.getStorage()).cacheName();

    // Initialize the first center to a random point.
    Vector sample = localCopyOf(points.viewRow(rnd.nextInt(ptsCnt)));

    List<Vector> centers = new ArrayList<>();
    List<Vector> newCenters = new ArrayList<>();
    newCenters.add(sample);
    centers.add(sample);

    final ConcurrentHashMap<Integer, Double> costs = new ConcurrentHashMap<>();

    // On each step, sample 2 * k points on average with probability proportional
    // to their squared distance from the centers. Note that only distances between points
    // and new centers are computed in each iteration.
    int step = 0;
    UUID uid = points.getUUID();

    while (step < initSteps) {
        // We assume here that costs can fit into memory of one node.
        ConcurrentHashMap<Integer, Double> newCosts = getNewCosts(points, newCenters, cacheName);

        // Merge costs with new costs.
        for (Integer ind : newCosts.keySet())
            costs.merge(ind, newCosts.get(ind), Math::min);

        double sumCosts = costs.values().stream().mapToDouble(Double::valueOf).sum();

        newCenters = getNewCenters(k, costs, uid, sumCosts, cacheName);
        centers.addAll(newCenters);

        step++;
    }

    List<Vector> distinctCenters = centers.stream().distinct().collect(Collectors.toList());

    if (distinctCenters.size() <= k)
        return distinctCenters.toArray(new Vector[] {});
    else {
        // Finally, we might have a set of more than k distinct candidate centers; weight each
        // candidate by the number of points in the dataset mapping to it and run a local k-means++
        // on the weighted centers to pick k of them
        ConcurrentHashMap<Integer, Integer> centerInd2Weight = weightCenters(uid, distinctCenters, cacheName);

        List<Double> weights = new ArrayList<>(centerInd2Weight.size());

        for (int i = 0; i < distinctCenters.size(); i++)
            weights.add(i, Double.valueOf(centerInd2Weight.getOrDefault(i, 0)));

        DenseLocalOnHeapMatrix dCenters = MatrixUtil.fromList(distinctCenters, true);

        return new KMeansLocalClusterer(getDistanceMeasure(), 30, seed).cluster(dCenters, k, weights).centers();
    }
}
 

import java.util.concurrent.ConcurrentHashMap; //导入方法依赖的package包/类
/**
 * Choose k primary centers from source points.
 *
 * @param points Matrix with source points.
 * @param k Number of centers.
 * @return Array of primary centers.
 */
private Vector[] initializeCenters(SparseDistributedMatrix points, int k) {
    int pointsNum = points.rowSize();

    Vector firstCenter = points.viewRow(rnd.nextInt(pointsNum));

    List<Vector> centers = new ArrayList<>();
    List<Vector> newCenters = new ArrayList<>();

    centers.add(firstCenter);
    newCenters.add(firstCenter);

    ConcurrentHashMap<Integer, Double> costs = new ConcurrentHashMap<>();

    int step = 0;
    UUID uuid = points.getUUID();
    String cacheName = ((SparseDistributedMatrixStorage) points.getStorage()).cacheName();

    while(step < initSteps) {
        ConcurrentHashMap<Integer, Double> newCosts = getNewCosts(cacheName, uuid, newCenters);

        for (Integer key : newCosts.keySet())
            costs.merge(key, newCosts.get(key), Math::min);

        double costsSum = costs.values().stream().mapToDouble(Double::valueOf).sum();

        newCenters = getNewCenters(cacheName, uuid, costs, costsSum, k);
        centers.addAll(newCenters);

        step++;
    }

    return chooseKCenters(cacheName, uuid, centers, k);
}