VFTransformBoxCox.java

/*
 * 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.data.filter.var;

import rapaio.data.Var;

/**
 * Created by <a href="mailto:padreati@yahoo.com">Aurelian Tutuianu</a> at 12/11/14.
 */
public class VFTransformBoxCox extends AbstractVF {

    private static final long serialVersionUID = 1914770412929840529L;
    private final double lambda;
    private final double shift;

    public VFTransformBoxCox(double lambda) {
        this(lambda, 0.0);
    }

    public VFTransformBoxCox(double lambda, double shift) {
        this.lambda = lambda;
        this.shift = shift;
    }

    public double lambda() {
        return lambda;
    }

    public double shift() {
        return shift;
    }

    @Override
    public void fit(Var... vars) {
        checkSingleVar(vars);
    }

    @Override
    public Var apply(Var... vars) {
        checkSingleVar(vars);

        return vars[0].stream().transValue(value -> {
            if (lambda == 0)
                return Math.log(value + shift);
            else
                return (Math.pow(value + shift, lambda) - 1) / lambda;
        }).toMappedVar();
    }
}