TwoStepMapper

All Known Subinterfaces:

TwoStepMapper.Combineable<T,R,A>, TwoStepMapper.Mergeable<T,R>

All Known Implementing Classes:

BatchNode.TwoStepWrapper, SampleSet.CombineableSet, TwoStepMapper.KeyCounter, TwoStepMapper.SimpleCache
```
public interface TwoStepMapper<T,R>
```
A TwoStepMapper is a mapper/reducer that is used in 2 steps – consume(Object) and getResults(). First you consume some (many) elements, then you get the results. The results is one instance of some aggregate type – most likely a collection or map containing derived information.
Resettable (to enable reuse).
There are 2 optional extensions to this interface: TwoStepMapper.Combineable and TwoStepMapper.Mergeable. The first enables combining the state of multiple instances. The second enables merging the results from multiple instances. The difference is that combining is done before the final results are calculated, while merging is done after the final results are calculated. If getResults() simply returns the internal state of the instance, unaltered, then combining and merging are identical.

Nested Class Summary

Nested Classes
Modifier and Type	Interface	Description
`static interface`	`TwoStepMapper.Combineable<T,R,A extends TwoStepMapper.Combineable<T,R,A>>`	Enables combining the state of multiple instances.
`static class`	`TwoStepMapper.KeyCounter<T,G>`	A frequency counter that optionally filters some elements when merging subresults.
`static interface`	`TwoStepMapper.Mergeable<T,R>`	Enables merging the results from multiple instances.
`static class`	`TwoStepMapper.SimpleCache<K,V>`	Will calculate the function value for each input item, and cache the result.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`consume(T item)`	Input/consume the items that should be mapped
`R`	`getResults()`	Output the mapped results
`void`	`reset()`	Reset, so it can be re-used

- Method Detail
  - consume
```
void consume(T item)
```
    Input/consume the items that should be mapped
  - getResults
```
R getResults()
```
    Output the mapped results
  - reset
```
void reset()
```
    Reset, so it can be re-used