public class StringReducer
A StringReducer is used to take a set of examples and reduce them.
The idea: suppose you have a large number of columns, and you want to combine/reduce the values in each column.
StringReducer allows you to specify different reductions for differently for different columns: min, max, sum, mean etc.
See StringReducer.Builder and ReduceOp for the full list.
(1) Reducing examples by a key
(2) Reduction operations in time series (windowing ops, etc)