/*
* Apache License
* Version 2.0, January 2004
* http://www.apache.org/licenses/
*
* Copyright 2013 Aurelian Tutuianu
* Copyright 2014 Aurelian Tutuianu
* Copyright 2015 Aurelian Tutuianu
* Copyright 2016 Aurelian Tutuianu
*
* 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 rapaio.ml.classifier.tree;
import rapaio.core.tests.ChiSquareTest;
import rapaio.core.tools.DTable;
import rapaio.util.Tagged;
import java.io.Serializable;
/**
* Created by <a href="mailto:padreati@yahoo.com>Aurelian Tutuianu</a>.
*/
public interface CTreePurityFunction extends Tagged, Serializable {
CTreePurityFunction InfoGain = new CTreePurityFunction() {
private static final long serialVersionUID = 152790997381399918L;
@Override
public double compute(DTable dt) {
return dt.splitByRowInfoGain();
}
@Override
public String name() {
return "InfoGain";
}
@Override
public String toString() {
return name();
}
};
CTreePurityFunction GainRatio = new CTreePurityFunction() {
private static final long serialVersionUID = -2478996054579932911L;
@Override
public String name() {
return "GainRatio";
}
@Override
public double compute(DTable dt) {
return dt.splitByRowGainRatio();
}
@Override
public String toString() {
return name();
}
};
CTreePurityFunction GiniGain = new CTreePurityFunction() {
private static final long serialVersionUID = 3547209320599654633L;
@Override
public String name() {
return "GiniGain";
}
@Override
public double compute(DTable dt) {
double[] rowTotals = new double[dt.rowLevels().length];
double[] colTotals = new double[dt.colLevels().length];
double total = 0.0;
for (int i = 0; i < dt.rowLevels().length; i++) {
// j = 1 just for optimization, we know that we should not have missing targets
for (int j = 1; j < dt.colLevels().length; j++) {
rowTotals[i] += dt.get(i, j);
if (i != 0) {
colTotals[j] += dt.get(i, j);
total += dt.get(i, j);
}
}
}
if (total <= 0) {
// no instances | all missing on test
return 0;
}
// compute before split gini impurity
double gini = 1.0;
for (int i = 1; i < dt.colLevels().length; i++) {
gini -= Math.pow(colTotals[i] / total, 2);
}
// compute after split gini impurity for each test level
for (int i = 1; i < dt.rowLevels().length; i++) {
double gini_k = 1;
for (int j = 1; j < dt.colLevels().length; j++) {
if (rowTotals[i] > 0)
gini_k -= Math.pow(dt.get(i, j) / rowTotals[i], 2);
}
gini -= gini_k * rowTotals[i] / total;
}
return gini * total / (total + rowTotals[0]);
}
@Override
public String toString() {
return name();
}
};
CTreePurityFunction ChiSquare = new CTreePurityFunction() {
private static final long serialVersionUID = 3547209320599654633L;
@Override
public String name() {
return "ChiSquare";
}
@Override
public double compute(DTable dt) {
return 1 - ChiSquareTest.independenceTest(dt).pValue();
}
@Override
public String toString() {
return name();
}
};
double compute(DTable dt);
}