Packages

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

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
  def bufferEncoder: Encoder[Int] = Encoders.scalaInt
  def outputEncoder: Encoder[Int] = Encoders.scalaInt
}.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.

Source
Aggregator.scala
Since

1.6.0

Linear Supertypes
Serializable, Serializable, AnyRef, Any
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Visibility
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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 output value type.

    Specifies the Encoder for the final output 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. 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