Hello,
I've implemented a program using map reduce for a simple distance
calculations between two 2D points. I've set up my input such that all
calculations should be the same but they are not. This makes me think I'm
doing something wrong within a map and/or reduce function. Here is my
output.
1,7,13,19 18.973665961010276
10,16,22,28 8.48528137423857
11,17,23,29 8.48528137423857
12,18,24,30 8.48528137423857
13,19,25,31 8.48528137423857
14,20,26,32 8.48528137423857
15,21,27,33 18.973665961010276
16,22,28,34 18.973665961010276
17,23,29,35 18.973665961010276
18,24,30,36 8.48528137423857
19,25,31,37 18.973665961010276
2,8,14,20 8.48528137423857
20,26,32,38 8.48528137423857
21,27,33,39 8.48528137423857
22,28,34,40 8.48528137423857
23,29,35,41 8.48528137423857
24,30,36,42 8.48528137423857
25,31,37,43 18.973665961010276
26,32,38,44 18.973665961010276
27,33,39,45 18.973665961010276
28,34,40,46 16.97056274847714
29,35,41,47 8.48528137423857
3,9,15,21 8.48528137423857
30,36,42,48 18.973665961010276
31,37,43,49 18.973665961010276
32,38,44,50 8.48528137423857
33,39,45,51 8.48528137423857
34,40,46,52 8.48528137423857
35,41,47,53 18.973665961010276
4,10,16,22 18.973665961010276
5,11,17,23 18.973665961010276
6,12,18,24 8.48528137423857
7,13,19,25 8.48528137423857
8,14,20,26 8.48528137423857
9,15,21,27 18.973665961010276
My key is the entire line entry of the input file and the value is the
distance calculated. Any value that doesn't begin with an 8 is wrong.
This is what I do in the mapper.
public static class Map extends MapReduceBase
implements Mapper<LongWritable, Text,
Text, DoubleWritable>
{
private Text word = new Text();
public void map(LongWritable key, Text value,
OutputCollector<Text, DoubleWritable> output,
Reporter reporter) throws IOException
{
String line = value.toString();
String[] tokens = line.split("[,]");
for(int i = 0; i < tokens.length; i++)
{
word.set(line);
output.collect(word, new
DoubleWritable(Double.parseDouble(tokens[i])));
}
}//public void map
}//public static class Map
And this is what I do in the reducer.
public static class Reduce extends MapReduceBase
implements Reducer<Text, DoubleWritable,
Text, DoubleWritable>
{
public void reduce(Text key, Iterator<DoubleWritable> values,
OutputCollector<Text, DoubleWritable> output, Reporter reporter)
throws IOException
{
double distance = 0;
double x1 = 0;
double x2 = 0;
double y1 = 0;
double y2 = 0;
if(values.hasNext())
{
x1 = values.next().get();
}
if(values.hasNext())
{
x2 = values.next().get();
}
if(values.hasNext())
{
y1 = values.next().get();
}
if(values.hasNext())
{
y2 = values.next().get();
}
distance = StrictMath.sqrt(StrictMath.pow(x2 - x1, 2.0) +
StrictMath.pow(y2 - y1, 2.0));
output.collect(key, new DoubleWritable(distance));
}
}//public static class Reduce
Any suggestions would be appreciated.
Erik
