org.apache.spark.sql.expressions

Aggregator

abstract class Aggregator[-IN, BUF, OUT] extends Serializable

:: Experimental :: A base class for user-defined aggregations, which can be used in Dataset operations to take all of the elements of a group and reduce them to a single value.

For example, the following aggregator extracts an int from a specific class and adds them up:

case class Data(i: Int)

val customSummer =  new Aggregator[Data, Int, Int] {
  def zero: Int = 0
  def reduce(b: Int, a: Data): Int = b + a.i
  def merge(b1: Int, b2: Int): Int = b1 + b2
  def finish(r: Int): Int = r
}.toColumn()

val ds: Dataset[Data] = ...
val aggregated = ds.select(customSummer)

Based loosely on Aggregator from Algebird: https://github.com/twitter/algebird

IN

The input type for the aggregation.

BUF

The type of the intermediate value of the reduction.

OUT

The type of the final output result.

Annotations
@Experimental() @Evolving()
Since

1.6.0

Linear Supertypes
Serializable, Serializable, AnyRef, Any
Known Subclasses
TypedAverage, TypedCount, TypedSumDouble, TypedSumLong
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Instance Constructors

  1. new Aggregator()

Abstract Value Members

  1. abstract def bufferEncoder: Encoder[BUF]

    Specifies the Encoder for the intermediate value type.

    Specifies the Encoder for the intermediate value type.

    Since

    2.0.0

  2. abstract def finish(reduction: BUF): OUT

    Transform the output of the reduction.

    Transform the output of the reduction.

    Since

    1.6.0

  3. abstract def merge(b1: BUF, b2: BUF): BUF

    Merge two intermediate values.

    Merge two intermediate values.

    Since

    1.6.0

  4. abstract def outputEncoder: Encoder[OUT]

    Specifies the Encoder for the final ouput value type.

    Specifies the Encoder for the final ouput value type.

    Since

    2.0.0

  5. abstract def reduce(b: BUF, a: IN): BUF

    Combine two values to produce a new value.

    Combine two values to produce a new value. For performance, the function may modify b and return it instead of constructing new object for b.

    Since

    1.6.0

  6. abstract def zero: BUF

    A zero value for this aggregation.

    A zero value for this aggregation. Should satisfy the property that any b + zero = b.

    Since

    1.6.0

Concrete Value Members

  1. final def !=(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef

  2. final def !=(arg0: Any): Boolean

    Definition Classes
    Any

  3. final def ##(): Int

    Definition Classes
    AnyRef → Any

  4. final def ==(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef

  5. final def ==(arg0: Any): Boolean

    Definition Classes
    Any

  6. final def asInstanceOf[T0]: T0

    Definition Classes
    Any

  7. def clone(): AnyRef

    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )

  8. final def eq(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef

  9. def equals(arg0: Any): Boolean

    Definition Classes
    AnyRef → Any

  10. def finalize(): Unit

    Attributes
    protected[java.lang]
    Definition Classes
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    Annotations
    @throws( classOf[java.lang.Throwable] )

  11. final def getClass(): Class[_]

    Definition Classes
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  12. def hashCode(): Int

    Definition Classes
    AnyRef → Any

  13. final def isInstanceOf[T0]: Boolean

    Definition Classes
    Any

  14. final def ne(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef

  15. final def notify(): Unit

    Definition Classes
    AnyRef

  16. final def notifyAll(): Unit

    Definition Classes
    AnyRef

  17. final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
    AnyRef

  18. def toColumn: TypedColumn[IN, OUT]

    Returns this Aggregator as a TypedColumn that can be used in Dataset.

    Returns this Aggregator as a TypedColumn that can be used in Dataset. operations.

    Since

    1.6.0

  19. def toString(): String

    Definition Classes
    AnyRef → Any

  20. final def wait(): Unit

    Definition Classes
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    @throws( ... )

  21. final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
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    @throws( ... )

  22. final def wait(arg0: Long): Unit

    Definition Classes
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    @throws( ... )

Inherited from Serializable

Inherited from Serializable

Inherited from AnyRef

Inherited from Any

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