package org.apache.mahout.clustering;
import java.util.List;
import com.google.common.base.Preconditions;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import org.apache.mahout.common.distance.DistanceMeasure;
import org.apache.mahout.common.distance.EuclideanDistanceMeasure;
import org.apache.mahout.math.Centroid;
import org.apache.mahout.math.DenseMatrix;
import org.apache.mahout.math.Matrix;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.WeightedVector;
import org.apache.mahout.math.neighborhood.BruteSearch;
import org.apache.mahout.math.neighborhood.ProjectionSearch;
import org.apache.mahout.math.neighborhood.Searcher;
import org.apache.mahout.math.neighborhood.UpdatableSearcher;
import org.apache.mahout.math.random.WeightedThing;
import org.apache.mahout.math.stats.OnlineSummarizer;
public final class ClusteringUtils {
private ClusteringUtils() {
}
/**
* Computes the summaries for the distances in each cluster.
* @param datapoints iterable of datapoints.
* @param centroids iterable of Centroids.
* @return a list of OnlineSummarizers where the i-th element is the summarizer corresponding to the cluster whose
* index is i.
*/
public static List<OnlineSummarizer> summarizeClusterDistances(Iterable<? extends Vector> datapoints,
Iterable<? extends Vector> centroids,
DistanceMeasure distanceMeasure) {
UpdatableSearcher searcher = new ProjectionSearch(distanceMeasure, 3, 1);
searcher.addAll(centroids);
List<OnlineSummarizer> summarizers = Lists.newArrayList();
if (searcher.size() == 0) {
return summarizers;
}
for (int i = 0; i < searcher.size(); ++i) {
summarizers.add(new OnlineSummarizer());
}
for (Vector v : datapoints) {
Centroid closest = (Centroid)searcher.search(v, 1).get(0).getValue();
OnlineSummarizer summarizer = summarizers.get(closest.getIndex());
summarizer.add(distanceMeasure.distance(v, closest));
}
return summarizers;
}
/**
* Adds up the distances from each point to its closest cluster and returns the sum.
* @param datapoints iterable of datapoints.
* @param centroids iterable of Centroids.
* @return the total cost described above.
*/
public static double totalClusterCost(Iterable<? extends Vector> datapoints, Iterable<? extends Vector> centroids) {
DistanceMeasure distanceMeasure = new EuclideanDistanceMeasure();
UpdatableSearcher searcher = new ProjectionSearch(distanceMeasure, 3, 1);
searcher.addAll(centroids);
return totalClusterCost(datapoints, searcher);
}
/**
* Adds up the distances from each point to its closest cluster and returns the sum.
* @param datapoints iterable of datapoints.
* @param centroids searcher of Centroids.
* @return the total cost described above.
*/
public static double totalClusterCost(Iterable<? extends Vector> datapoints, Searcher centroids) {
double totalCost = 0;
for (Vector vector : datapoints) {
totalCost += centroids.searchFirst(vector, false).getWeight();
}
return totalCost;
}
/**
* Estimates the distance cutoff. In StreamingKMeans, the distance between two vectors divided
* by this value is used as a probability threshold when deciding whether to form a new cluster
* or not.
* Small values (comparable to the minimum distance between two points) are preferred as they
* guarantee with high likelihood that all but very close points are put in separate clusters
* initially. The clusters themselves are actually collapsed periodically when their number goes
* over the maximum number of clusters and the distanceCutoff is increased.
* So, the returned value is only an initial estimate.
* @param data the datapoints whose distance is to be estimated.
* @param distanceMeasure the distance measure used to compute the distance between two points.
* @return the minimum distance between the first sampleLimit points
* @see org.apache.mahout.clustering.streaming.cluster.StreamingKMeans#clusterInternal(Iterable, boolean)
*/
public static double estimateDistanceCutoff(List<? extends Vector> data, DistanceMeasure distanceMeasure) {
BruteSearch searcher = new BruteSearch(distanceMeasure);
searcher.addAll(data);
double minDistance = Double.POSITIVE_INFINITY;
for (Vector vector : data) {
double closest = searcher.searchFirst(vector, true).getWeight();
if (minDistance > 0 && closest < minDistance) {
minDistance = closest;
}
searcher.add(vector);
}
return minDistance;
}
public static double estimateDistanceCutoff(Iterable<? extends Vector> data, DistanceMeasure distanceMeasure,
int sampleLimit) {
return estimateDistanceCutoff(Lists.newArrayList(Iterables.limit(data, sampleLimit)), distanceMeasure);
}
/**
* Computes the Davies-Bouldin Index for a given clustering.
* See http://en.wikipedia.org/wiki/Clustering_algorithm#Internal_evaluation
* @param centroids list of centroids
* @param distanceMeasure distance measure for inter-cluster distances
* @param clusterDistanceSummaries summaries of the clusters; See summarizeClusterDistances
* @return the Davies-Bouldin Index
*/
public static double daviesBouldinIndex(List<? extends Vector> centroids, DistanceMeasure distanceMeasure,
List<OnlineSummarizer> clusterDistanceSummaries) {
Preconditions.checkArgument(centroids.size() == clusterDistanceSummaries.size(),
"Number of centroids and cluster summaries differ.");
int n = centroids.size();
double totalDBIndex = 0;
// The inner loop shouldn't be reduced for j = i + 1 to n because the computation of the Davies-Bouldin
// index is not really symmetric.
// For a given cluster i, we look for a cluster j that maximizes the ratio of the sum of average distances
// from points in cluster i to its center and and points in cluster j to its center to the distance between
// cluster i and cluster j.
// The maximization is the key issue, as the cluster that maximizes this ratio might be j for i but is NOT
// NECESSARILY i for j.
for (int i = 0; i < n; ++i) {
double averageDistanceI = clusterDistanceSummaries.get(i).getMean();
double maxDBIndex = 0;
for (int j = 0; j < n; ++j) {
if (i != j) {
double dbIndex = (averageDistanceI + clusterDistanceSummaries.get(j).getMean())
/ distanceMeasure.distance(centroids.get(i), centroids.get(j));
if (dbIndex > maxDBIndex) {
maxDBIndex = dbIndex;
}
}
}
totalDBIndex += maxDBIndex;
}
return totalDBIndex / n;
}
/**
* Computes the Dunn Index of a given clustering. See http://en.wikipedia.org/wiki/Dunn_index
* @param centroids list of centroids
* @param distanceMeasure distance measure to compute inter-centroid distance with
* @param clusterDistanceSummaries summaries of the clusters; See summarizeClusterDistances
* @return the Dunn Index
*/
public static double dunnIndex(List<? extends Vector> centroids, DistanceMeasure distanceMeasure,
List<OnlineSummarizer> clusterDistanceSummaries) {
Preconditions.checkArgument(centroids.size() == clusterDistanceSummaries.size(),
"Number of centroids and cluster summaries differ.");
int n = centroids.size();
// Intra-cluster distances will come from the OnlineSummarizer, and will be the median distance (noting that
// the median for just one value is that value).
// A variety of metrics can be used for the intra-cluster distance including max distance between two points,
// mean distance, etc. Median distance was chosen as this is more robust to outliers and characterizes the
// distribution of distances (from a point to the center) better.
double maxIntraClusterDistance = 0;
for (OnlineSummarizer summarizer : clusterDistanceSummaries) {
if (summarizer.getCount() > 0) {
double intraClusterDistance;
if (summarizer.getCount() == 1) {
intraClusterDistance = summarizer.getMean();
} else {
intraClusterDistance = summarizer.getMedian();
}
if (maxIntraClusterDistance < intraClusterDistance) {
maxIntraClusterDistance = intraClusterDistance;
}
}
}
double minDunnIndex = Double.POSITIVE_INFINITY;
for (int i = 0; i < n; ++i) {
// Distances are symmetric, so d(i, j) = d(j, i).
for (int j = i + 1; j < n; ++j) {
double dunnIndex = distanceMeasure.distance(centroids.get(i), centroids.get(j));
if (minDunnIndex > dunnIndex) {
minDunnIndex = dunnIndex;
}
}
}
return minDunnIndex / maxIntraClusterDistance;
}
public static double choose2(double n) {
return n * (n - 1) / 2;
}
/**
* Creates a confusion matrix by searching for the closest cluster of both the row clustering and column clustering
* of a point and adding its weight to that cell of the matrix.
* It doesn't matter which clustering is the row clustering and which is the column clustering. If they're
* interchanged, the resulting matrix is the transpose of the original one.
* @param rowCentroids clustering one
* @param columnCentroids clustering two
* @param datapoints datapoints whose closest cluster we need to find
* @param distanceMeasure distance measure to use
* @return the confusion matrix
*/
public static Matrix getConfusionMatrix(List<? extends Vector> rowCentroids, List<? extends Vector> columnCentroids,
Iterable<? extends Vector> datapoints, DistanceMeasure distanceMeasure) {
Searcher rowSearcher = new BruteSearch(distanceMeasure);
rowSearcher.addAll(rowCentroids);
Searcher columnSearcher = new BruteSearch(distanceMeasure);
columnSearcher.addAll(columnCentroids);
int numRows = rowCentroids.size();
int numCols = columnCentroids.size();
Matrix confusionMatrix = new DenseMatrix(numRows, numCols);
for (Vector vector : datapoints) {
WeightedThing<Vector> closestRowCentroid = rowSearcher.search(vector, 1).get(0);
WeightedThing<Vector> closestColumnCentroid = columnSearcher.search(vector, 1).get(0);
int row = ((Centroid) closestRowCentroid.getValue()).getIndex();
int column = ((Centroid) closestColumnCentroid.getValue()).getIndex();
double vectorWeight;
if (vector instanceof WeightedVector) {
vectorWeight = ((WeightedVector) vector).getWeight();
} else {
vectorWeight = 1;
}
confusionMatrix.set(row, column, confusionMatrix.get(row, column) + vectorWeight);
}
return confusionMatrix;
}
/**
* Computes the Adjusted Rand Index for a given confusion matrix.
* @param confusionMatrix confusion matrix; not to be confused with the more restrictive ConfusionMatrix class
* @return the Adjusted Rand Index
*/
public static double getAdjustedRandIndex(Matrix confusionMatrix) {
int numRows = confusionMatrix.numRows();
int numCols = confusionMatrix.numCols();
double rowChoiceSum = 0;
double columnChoiceSum = 0;
double totalChoiceSum = 0;
double total = 0;
for (int i = 0; i < numRows; ++i) {
double rowSum = 0;
for (int j = 0; j < numCols; ++j) {
rowSum += confusionMatrix.get(i, j);
totalChoiceSum += choose2(confusionMatrix.get(i, j));
}
total += rowSum;
rowChoiceSum += choose2(rowSum);
}
for (int j = 0; j < numCols; ++j) {
double columnSum = 0;
for (int i = 0; i < numRows; ++i) {
columnSum += confusionMatrix.get(i, j);
}
columnChoiceSum += choose2(columnSum);
}
double rowColumnChoiceSumDivTotal = rowChoiceSum * columnChoiceSum / choose2(total);
return (totalChoiceSum - rowColumnChoiceSumDivTotal)
/ ((rowChoiceSum + columnChoiceSum) / 2 - rowColumnChoiceSumDivTotal);
}
/**
* Computes the total weight of the points in the given Vector iterable.
* @param data iterable of points
* @return total weight
*/
public static double totalWeight(Iterable<? extends Vector> data) {
double sum = 0;
for (Vector row : data) {
Preconditions.checkNotNull(row);
if (row instanceof WeightedVector) {
sum += ((WeightedVector)row).getWeight();
} else {
sum++;
}
}
return sum;
}
}