The combiner works across multiple invocations of the map function and may be applied on the reduce side as well.
Sent from my iPhone On Jul 18, 2011, at 13:32, Sean Owen <[email protected]> wrote: > I don't think the mapper can do any 'combining' on its own though > before emitting, if that's what you're suggesting. Within one map you > are touching one column; there is nothing from the map's output by > itself that can be summed before writing, because every co-occurrence > is from a different item-item pair.
