## cascading.operation.aggregator
Class ExtremaValueBase

    java.lang.Object
      cascading.operation.BaseOperation<ExtremaValueBase.Context>
          cascading.operation.aggregator.ExtremaValueBase

All Implemented Interfaces:
  DeclaresResults, Aggregator<ExtremaValueBase.Context>, Operation<ExtremaValueBase.Context>, Traceable, Serializable

Direct Known Subclasses:
  MaxValue, MinValue

    public abstract class ExtremaValueBase

extends BaseOperation<ExtremaValueBase.Context>
implements Aggregator<ExtremaValueBase.Context>

Class ExtremaValueBase is the base class for MaxValue and MinValue where the values are expected to by `Comparable` types and the `Comparable.compareTo(Object)` result is use for max/min comparison.

See Also:
  Serialized Form

Nested Class Summary
`protected static class` `ExtremaValueBase.Context`

Field Summary
`protected Collection` `ignoreValues` Field ignoreValues

Fields inherited from class cascading.operation.BaseOperation
`fieldDeclaration, numArgs, trace`

Fields inherited from interface cascading.operation.Operation
`ANY`

Constructor Summary
`` `ExtremaValueBase(Fields fieldDeclaration)`
`protected` `ExtremaValueBase(Fields fieldDeclaration, Object... ignoreValues)`
`` `ExtremaValueBase(int numArgs, Fields fieldDeclaration)`

Method Summary
`void` `aggregate(FlowProcess flowProcess, AggregatorCall<ExtremaValueBase.Context> aggregatorCall)` Method aggregate is called for each `TupleEntry` value in the current grouping.
`protected abstract boolean` `compare(Comparable lhs, Comparable rhs)` Allows subclasses to provide own comparison method.
`void` `complete(FlowProcess flowProcess, AggregatorCall<ExtremaValueBase.Context> aggregatorCall)` Method complete will be issued last after every `TupleEntry` has been passed to the `Aggregator.aggregate(cascading.flow.FlowProcess, AggregatorCall)` method.
`boolean` `equals(Object object)`
`Collection` `getIgnoreValues()`
`protected Tuple` `getResult(AggregatorCall<ExtremaValueBase.Context> aggregatorCall)`
`int` `hashCode()`
`void` `prepare(FlowProcess flowProcess, OperationCall<ExtremaValueBase.Context> operationCall)` Method prepare does nothing, and may safely be overridden.
`void` `start(FlowProcess flowProcess, AggregatorCall<ExtremaValueBase.Context> aggregatorCall)` Method start initializes the aggregation procedure and is called for every unique grouping.

Methods inherited from class cascading.operation.BaseOperation
`cleanup, flush, getFieldDeclaration, getNumArgs, getTrace, isSafe, printOperationInternal, toString, toStringInternal`

Methods inherited from class java.lang.Object
`clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

Methods inherited from interface cascading.operation.Operation
`cleanup, flush, getFieldDeclaration, getNumArgs, isSafe`

Field Detail

### ignoreValues

    protected final Collection ignoreValues

  Field ignoreValues

Constructor Detail

### ExtremaValueBase

    @ConstructorProperties(value="fieldDeclaration")
    public ExtremaValueBase(Fields fieldDeclaration)

### ExtremaValueBase

    @ConstructorProperties(value={"numArgs","fieldDeclaration"})
    public ExtremaValueBase(int numArgs,
                                                       Fields fieldDeclaration)

### ExtremaValueBase

    @ConstructorProperties(value={"fieldDeclaration","ignoreValues"})
    protected ExtremaValueBase(Fields fieldDeclaration,
                                                          Object... ignoreValues)

Method Detail

### getIgnoreValues

    public Collection getIgnoreValues()

### prepare

    public void prepare(FlowProcess flowProcess,
                        OperationCall<ExtremaValueBase.Context> operationCall)

  Description copied from class: `BaseOperation`
  Method prepare does nothing, and may safely be overridden.

  Specified by:
    `prepare` in interface `Operation<ExtremaValueBase.Context>`
  Overrides:
    `prepare` in class `BaseOperation<ExtremaValueBase.Context>`

### start

    public void start(FlowProcess flowProcess,
                      AggregatorCall<ExtremaValueBase.Context> aggregatorCall)

  Description copied from interface: `Aggregator`
  Method start initializes the aggregation procedure and is called for every unique grouping.

  The AggregatorCall context should be initialized here if necessary.

  The first time this method is called for a given 'process', the AggregatorCall context will be null. This method should set a new instance of the user defined context object. When the AggregatorCall context is not null, it is up to the developer to create a new instance, or 'recycle' the given instance. If recycled, it must be re-initialized to remove any previous state/values.

  For example, if a Map is used to hold the intermediate data for each subsequent `Aggregator.aggregate(cascading.flow.FlowProcess, AggregatorCall)` call, new HashMap() should be set on the AggregatorCall instance when `OperationCall.getContext()` is null. On the next grouping, start() will be called again, but this time with the old Map instance. In this case, map.clear() should be invoked before returning.

  Specified by:
    `start` in interface `Aggregator<ExtremaValueBase.Context>`
  Parameters:
    `flowProcess` - of type FlowProcess
    `aggregatorCall` - of type AggregatorCall

### aggregate

    public void aggregate(FlowProcess flowProcess,
                          AggregatorCall<ExtremaValueBase.Context> aggregatorCall)

  Description copied from interface: `Aggregator`
  Method aggregate is called for each `TupleEntry` value in the current grouping.

  TupleEntry entry, or entry.getTuple() should not be stored directly in the context. A copy of the tuple should be made via the `new Tuple( entry.getTuple() )` copy constructor.

  Specified by:
    `aggregate` in interface `Aggregator<ExtremaValueBase.Context>`
  Parameters:
    `flowProcess` - of type FlowProcess
    `aggregatorCall` - of type AggregatorCall

### compare

    protected abstract boolean compare(Comparable lhs,
                                       Comparable rhs)

  Allows subclasses to provide own comparison method.

  Parameters:
    `lhs` - Comparable type
    `rhs` - Comparable type
  Returns:
    true if the rhs should be retained as the result value

### complete

    public void complete(FlowProcess flowProcess,
                         AggregatorCall<ExtremaValueBase.Context> aggregatorCall)

  Description copied from interface: `Aggregator`
  Method complete will be issued last after every `TupleEntry` has been passed to the `Aggregator.aggregate(cascading.flow.FlowProcess, AggregatorCall)` method. Any final calculation should be completed here and passed to the outputCollector.

  Specified by:
    `complete` in interface `Aggregator<ExtremaValueBase.Context>`
  Parameters:
    `flowProcess` - of type FlowProcess
    `aggregatorCall` - of type AggregatorCall

### getResult

    protected Tuple getResult(AggregatorCall<ExtremaValueBase.Context> aggregatorCall)

### equals

    public boolean equals(Object object)

  Overrides:
    `equals` in class `BaseOperation<ExtremaValueBase.Context>`

### hashCode

    public int hashCode()

  Overrides:
    `hashCode` in class `BaseOperation<ExtremaValueBase.Context>`

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