org.apache.mahout.math.stats.entropy.CalculateEntropyMapper.java Source code

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Here is the source code for org.apache.mahout.math.stats.entropy.CalculateEntropyMapper.java

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/**
 * 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.mahout.math.stats.entropy;

import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.mahout.math.VarIntWritable;

import java.io.IOException;

/**
 * Calculates the entropy for the value with H(x) = x * log(x)
 */
public final class CalculateEntropyMapper extends Mapper<Text, VarIntWritable, NullWritable, DoubleWritable> {

    private final DoubleWritable result = new DoubleWritable();

    @Override
    protected void map(Text key, VarIntWritable value, Context context) throws IOException, InterruptedException {
        result.set(value.get() * Math.log(value.get()));
        context.write(NullWritable.get(), result);
    }

}