Package org.apache.beam.sdk.transforms

Class Combine.Globally<InputT,​OutputT>

  • Type Parameters:
    InputT - type of input values
    OutputT - type of output values
    All Implemented Interfaces:
    java.io.Serializable, HasDisplayData
    Enclosing class:
    Combine
    public static class Combine.Globally<InputT,​OutputT>
extends PTransform<PCollection<InputT>,​PCollection<OutputT>>
    Combine.Globally<InputT, OutputT> takes a PCollection<InputT> and returns a PCollection<OutputT> whose elements are the result of combining all the elements in each window of the input PCollection, using a specified CombineFn<InputT, AccumT, OutputT>. It is common for InputT == OutputT, but not required. Common combining functions include sums, mins, maxes, and averages of numbers, conjunctions and disjunctions of booleans, statistical aggregations, etc.

    Example of use: 

    
 PCollection<Integer> pc = ...;
 PCollection<Integer> sum = pc.apply(
     Combine.globally(new Sum.SumIntegerFn()));

    Combining can happen in parallel, with different subsets of the input PCollection being combined separately, and their intermediate results combined further, in an arbitrary tree reduction pattern, until a single result value is produced.

    If the input PCollection is windowed into GlobalWindows, a default value in the GlobalWindow will be output if the input PCollection is empty. To use this with inputs with other windowing, either withoutDefaults() or asSingletonView() must be called, as the default value cannot be automatically assigned to any single window.

    By default, the Coder of the output PValue<OutputT> is inferred from the concrete type of the CombineFn<InputT, AccumT, OutputT>'s output type OutputT.

    See also Combine.perKey(org.apache.beam.sdk.transforms.SerializableFunction<java.lang.Iterable<V>, V>)/Combine.PerKey and Combine.groupedValues(org.apache.beam.sdk.transforms.SerializableFunction<java.lang.Iterable<V>, V>)/Combine.GroupedValues, which are useful for combining values associated with each key in a PCollection of KVs.

    See Also:
    Serialized Form

    • Method Detail

      • getKindString

        protected java.lang.String getKindString()
        Description copied from class: PTransform
        Returns the name to use by default for this PTransform (not including the names of any enclosing PTransforms).

        By default, returns the base name of this PTransform's class.

        The caller is responsible for ensuring that names of applied PTransforms are unique, e.g., by adding a uniquifying suffix when needed.

        Overrides:
        getKindString in class PTransform<PCollection<InputT>,​PCollection<OutputT>>

      • asSingletonView

        public Combine.GloballyAsSingletonView<InputT,​OutputT> asSingletonView()
        Returns a PTransform that produces a PCollectionView whose elements are the result of combining elements per-window in the input PCollection. If a value is requested from the view for a window that is not present, the result of applying the CombineFn to an empty input set will be returned.

      • withoutDefaults

        public Combine.Globally<InputT,​OutputT> withoutDefaults()
        Returns a PTransform identical to this, but that does not attempt to provide a default value in the case of empty input. Required when the input is not globally windowed and the output is not being used as a side input.

      • withFanout

        public Combine.Globally<InputT,​OutputT> withFanout​(int fanout)
        Returns a PTransform identical to this, but that uses an intermediate node to combine parts of the data to reduce load on the final global combine step.

        The fanout parameter determines the number of intermediate keys that will be used.

      • getSideInputs

        public java.util.List<PCollectionView<?>> getSideInputs()
        Returns the side inputs used by this Combine operation.

      • isInsertDefault

        public boolean isInsertDefault()
        Returns whether or not this transformation applies a default value.

      • expand

        public PCollection<OutputT> expand​(PCollection<InputT> input)
        Description copied from class: PTransform
        Override this method to specify how this PTransform should be expanded on the given InputT.

        NOTE: This method should not be called directly. Instead apply the PTransform should be applied to the InputT using the apply method.

        Composite transforms, which are defined in terms of other transforms, should return the output of one of the composed transforms. Non-composite transforms, which do not apply any transforms internally, should return a new unbound output and register evaluators (via backend-specific registration methods).

        Specified by:
        expand in class PTransform<PCollection<InputT>,​PCollection<OutputT>>

      • populateDisplayData

        public void populateDisplayData​(DisplayData.Builder builder)
        Description copied from class: PTransform
        Register display data for the given transform or component.

        populateDisplayData(DisplayData.Builder) is invoked by Pipeline runners to collect display data via DisplayData.from(HasDisplayData). Implementations may call super.populateDisplayData(builder) in order to register display data in the current namespace, but should otherwise use subcomponent.populateDisplayData(builder) to use the namespace of the subcomponent.

        By default, does not register any display data. Implementors may override this method to provide their own display data.

        Specified by:
        populateDisplayData in interface HasDisplayData
        Overrides:
        populateDisplayData in class PTransform<PCollection<InputT>,​PCollection<OutputT>>
        Parameters:
        builder - The builder to populate with display data.
        See Also:
        HasDisplayData