Here's how to pass back a float value via a counter ...
First, in the first reducer, transform the float value into a long by multiplying by 1000 (to maintain 3 digits of precision, for example) and putting the result into a counter:
public void cleanup(Context context) {
long result = (long) (floatValue * 1000);
context.getCounter("Result","Result").increment(result);
}
In the driver class, retrieve the long value and transform it back to a float:
public static void MR1(String inputPath)
throws IOException, InterruptedException, ClassNotFoundException {
Configuration conf = new Configuration();
Job job = new Job(conf, "This is job1");
job.setJarByClass(MyProgram.class);
job.setMapperClass(MyMapper1.class);
job.setReducerClass(MyReduce1.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(FloatWritable.class);
FileInputFormat.addInputPath(job, new Path(inputPath));
job.waitForCompletion(true);
long result = job.getCounters().findCounter("Result","Result").getValue();
float value = ((float)result) / 1000;
}