package org.apache.mahout.math.hadoop.stats;
/**
* 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.
*/
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;
public class StandardDeviationCalculatorMapper extends
Mapper<IntWritable, Writable, IntWritable, DoubleWritable> {
public static final IntWritable SUM_OF_SQUARES = new IntWritable(1);
public static final IntWritable SUM = new IntWritable(2);
public static final IntWritable TOTAL_COUNT = new IntWritable(-1);
@Override
protected void map(IntWritable key, Writable value, Context context)
throws IOException, InterruptedException {
if (key.get() == -1) {
return;
}
//Kind of ugly, but such is life
double df = Double.NaN;
if (value instanceof LongWritable){
df = ((LongWritable)value).get();
} else if (value instanceof DoubleWritable) {
df = ((DoubleWritable)value).get();
}
if (!Double.isNaN(df)) {
// For calculating the sum of squares
context.write(SUM_OF_SQUARES, new DoubleWritable(df * df));
context.write(SUM, new DoubleWritable(df));
// For calculating the total number of entries
context.write(TOTAL_COUNT, new DoubleWritable(1));
}
}
}