Average/median/standard deviation

This is similar to min/max/count, but not as straightforward an implementation because these operations are not associative. A combiner can be used for all three, but requires a more complex approach than just reusing the reducer implementation.

A minimum, maximum, and count example, calculating the minimum, maximum, and count of a given field, are all excellent applications of the numerical summarization pattern.

SingleMapperReducer job seen earlier is a good example for aggregation pattern.

Depending on the use case, an aggregation pattern can be customized to generate the intended output.