BinomialSamplerMapper.java Source code

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Here is the source code for BinomialSamplerMapper.java

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/*
 * Copyright 2012-14 Justin A. Debrabant <debrabant@cs.brown.edu> and Matteo Riondato <matteo@cs.brown.edu>
 *
 * 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.
 *
 */

import java.io.IOException;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.Mapper;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reporter;

import cern.jet.random.Binomial;

public class BinomialSamplerMapper extends MapReduceBase implements Mapper<LongWritable, Text, IntWritable, Text> {
    private int reducersNum;
    private int datasetSize;

    @Override
    public void configure(JobConf conf) {
        reducersNum = conf.getInt("PARMM.reducersNum", 64);
        datasetSize = conf.getInt("PARMM.datasetSize", 1000);
    }

    @Override
    public void map(LongWritable lineNum, Text value, OutputCollector<IntWritable, Text> output, Reporter reporter)
            throws IOException {
        for (int i = 0; i < reducersNum; i++) {
            int sampledTimes = Binomial.staticNextInt(datasetSize / reducersNum, 1.0 / datasetSize);
            /**
             * XXX I assume there is a better way of doing
             * this, by only having one "message" sent to
             * reducer i, for example by making "value" an
             * object containing the fields "sampleTimes"
             * and "value". MR
             */
            for (int j = 0; j < sampledTimes; j++) {
                output.collect(new IntWritable(i), value);
            }
        }
    }
}