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## cascading.operation.aggregator
Class First

    java.lang.Object
      cascading.operation.BaseOperation<Tuple[]>
          cascading.operation.aggregator.ExtentBase
              cascading.operation.aggregator.First

All Implemented Interfaces:
  Aggregator<Tuple[]>, Operation<Tuple[]>, Serializable

    public class First

extends ExtentBase

Class First is an `Aggregator` that returns the first `Tuple` encountered in a grouping.

By default, it returns the first Tuple of `Fields.ARGS` found.

If `firstN` is given, Tuples with each of the first N number of Tuples encountered are returned. That is, this Aggregator will return at maximum N tuples per grouping.

Be sure to set the `GroupBy` `sortFields` to control which Tuples are seen first.

See Also:
  Serialized Form

Field Summary

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

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

Constructor Summary
`First()` Selects and returns the first argument Tuple encountered.
`First(Fields fieldDeclaration)` Selects and returns the first argument Tuple encountered.
`First(Fields fieldDeclaration, int firstN)` Selects and returns the first N argument Tuples encountered.
`First(Fields fieldDeclaration, Tuple... ignoreTuples)` Selects and returns the first argument Tuple encountered, unless the Tuple is a member of the set ignoreTuples.
`First(int firstN)` Selects and returns the first N argument Tuples encountered.

Method Summary
`void` | `complete(FlowProcess flowProcess, AggregatorCall<Tuple[]> aggregatorCall)` Method complete will be issued last after every `TupleEntry` has been passed to the `Aggregator.aggregate(cascading.flow.FlowProcess, AggregatorCall)` method.
`int` | `getFirstN()`
`protected void` | `performOperation(Tuple[] context, TupleEntry entry)`

Methods inherited from class cascading.operation.aggregator.ExtentBase
`aggregate, equals, getIgnoreTuples, getResult, hashCode, prepare, start`

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`

Constructor Detail

### First

    public First()

  Selects and returns the first argument Tuple encountered.

### First

    @ConstructorProperties(value="firstN")
    public First(int firstN)

  Selects and returns the first N argument Tuples encountered.

  Parameters:
    `firstN` - of type int

### First

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

  Selects and returns the first argument Tuple encountered.

  Parameters:
    `fieldDeclaration` - of type Fields

### First

    @ConstructorProperties(value={"fieldDeclaration","firstN"})
    public First(Fields fieldDeclaration,
                                            int firstN)

  Selects and returns the first N argument Tuples encountered.

  Parameters:
    `fieldDeclaration` - of type Fields
    `firstN` - of type int

### First

    @ConstructorProperties(value={"fieldDeclaration","ignoreTuples"})
    public First(Fields fieldDeclaration,
                                            Tuple... ignoreTuples)

  Selects and returns the first argument Tuple encountered, unless the Tuple is a member of the set ignoreTuples.

  Parameters:
    `fieldDeclaration` - of type Fields
    `ignoreTuples` - of type Tuple...

Method Detail

### getFirstN

    public int getFirstN()

### performOperation

    protected void performOperation(Tuple[] context,
                                    TupleEntry entry)

  Specified by:
    `performOperation` in class `ExtentBase`

### complete

    public void complete(FlowProcess flowProcess,
                         AggregatorCall<Tuple[]> 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<Tuple[]>`
  Overrides:
    `complete` in class `ExtentBase`
  Parameters:
    `flowProcess` - of type FlowProcess
    `aggregatorCall` - of type AggregatorCall

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