On Sep 9, 2008, at 12:20 PM, Shirley Cohen wrote:
I have a simple reducer that computes the average by doing a sum/
count. But I want to output both the average and the count for a
given key, not just the average. Is it possible to output both
values from the same invocation of the reducer? Or do I need two
reducer invocations? If I try to call output.collect() twice from
the reducer and label the key with "type=avg" or "type=count", I get
a bunch of garbage out. Please let me know if you have any
suggestions.
I'd be tempted to define a type like:
class AverageAndCount implements Writable {
private long sum;
private long count;
...
public String toString() {
return "avg = " + (sum / (double) count) + ", count = " + count);
}
}
Then you could use your reducer as both a combiner and reducer and you
would get both values out if you use TextOutputFormat. That said, it
should absolutely work to do collect twice.
-- Owen
