커다란 리듀스

public class CommaSeparateStringReduce extends MapReduceBase implements
		Reducer<Text, Text, Text, Text> {

	@Override
	public void reduce(Text key, Iterator<Text> values,
			OutputCollector<Text, Text> output, Reporter reporter)
			throws IOException {
		StringBuilder builder = new StringBuilder();
		while (values.hasNext()) {
			builder.append(values.next().toString());
			builder.append(",");
		}

		String result = builder.toString();
		result = result.substring(0, result.length() - 1);

		output.collect(key, new Text(result));
	}

}