Reduce can't change type of "Key" class?

[tim robertson <ti...@gmail.com>]

Hi all,

I am trying to do a map which emits:
- Key<MyKeyType>
- Value<Text>

and then reduce that emits
- Key<Text>
- Values of type<Text>

It blows up after a few reductions with:
java.io.IOException: wrong key class: class org.apache.hadoop.io.Text
is not class com.blah.blah.MyKeyType

I can understand why... but is there a work around for this?
(I do want to do this since the conversion is an expensive operation,
and by doing it in the reduction, I can do it once for the group...)
Maybe a Combiner that runs exactly once and does the conversion and
then a different reducer?  Is it possible?

Thanks for any help / insights

Tim