@ Override public List < List < O > > finish ( Collection < ? extends OutputWriter < O > > writers ) { ImmutableList . Builder < List < O >> out = ImmutableList . builder ( ) ; for ( OutputWriter < O > w : writers ) { InMemoryOutputWriter < O > writer = ( InMemoryOutputWriter < O > ) w ; out . add ( ImmutableList . copyOf ( writer . getResult ( ) ) ) ; } return out . build ( ) ; }
Returns a list of lists where the outer list has one element for each reduce shard which is a list of the values emitted by that shard in order .