com.insightml.evaluation.functions.Gini.java Source code

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Here is the source code for com.insightml.evaluation.functions.Gini.java

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/*
 * Copyright (C) 2016 Stefan Hen
 *
 * Licensed 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 com.insightml.evaluation.functions;

import java.util.Collections;
import java.util.LinkedList;
import java.util.List;

import org.apache.commons.math3.stat.descriptive.DescriptiveStatistics;
import org.apache.commons.math3.util.Pair;

import com.insightml.data.samples.ISamples;

final class Gini extends AbstractIndependentLabelsObjectiveFunction<Object, Object> {

    private static final long serialVersionUID = -3739867099887892986L;

    private final boolean normalize;

    Gini(final boolean normalize) {
        this.normalize = normalize;
    }

    @Override
    public DescriptiveStatistics label(final Object[] preds, final Object[] expected, final double[] weights,
            final ISamples<?, ?> samples, final int labelIndex) {
        final double gini = gini(preds, expected, false);
        return new DescriptiveStatistics(new double[] { normalize ? gini / gini(preds, expected, true) : gini, });
    }

    private static <T> double gini(final T[] preds, final Object[] expected, final boolean doPerfect) {
        final List<Pair<Object, T>> sortedByPdesc = new LinkedList<>();
        for (int i = 0; i < preds.length; ++i) {
            sortedByPdesc.add(new Pair<>(expected[i], preds[i]));
        }
        final boolean isBinary = sortedByPdesc.get(0).getSecond() instanceof Boolean;
        Collections.sort(sortedByPdesc, (o1, o2) -> {
            if (doPerfect) {
                if (isBinary) {
                    return ((Boolean) o1.getFirst()).booleanValue() ? -1 : 1;
                }
                return (Double) o1.getFirst() >= (Double) o2.getFirst() ? -1 : 1;
            }
            return (Double) o1.getSecond() >= (Double) o2.getSecond() ? -1 : 1;
        });

        double sum = 0;
        double giniSum = 0;
        for (final Pair<Object, T> prediction : sortedByPdesc) {
            if (isBinary) {
                sum += (Boolean) prediction.getFirst() ? 1 : 0;
            } else {
                sum += (Double) prediction.getFirst();
            }
            giniSum += sum;
        }

        giniSum = giniSum / sum - (sortedByPdesc.size() + 1.0) / 2;
        return giniSum / sortedByPdesc.size();
    }

}