ClusterEvaluator.java
- /*
- * 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.commons.math4.legacy.ml.clustering;
- import java.util.List;
- /**
- * Defines a measure of the quality of clusters.
- */
- public interface ClusterEvaluator {
- /**
- * @param cList List of clusters.
- * @return the score attributed by the evaluator.
- */
- double score(List<? extends Cluster<? extends Clusterable>> cList);
- /**
- * Provides a means to interpret the {@link #score(List) score value}.
- *
- * @param a Score computed by this evaluator.
- * @param b Score computed by this evaluator.
- * @return {@code true} if the evaluator considers that score
- * {@code a} is better than score {@code b}.
- */
- boolean isBetterScore(double a, double b);
- /**
- * Converts to a {@link ClusterRanking ranking function}
- * (as required by clustering implementations).
- *
- * @param <T> the type of points that can be clustered
- * @param eval Evaluator function.
- * @return a ranking function.
- */
- static <T extends Clusterable> ClusterRanking ranking(ClusterEvaluator eval) {
- return eval.isBetterScore(1, 2) ?
- clusters -> 1 / eval.score(clusters) :
- clusters -> eval.score(clusters);
- }
- }