Package org.apache.beam.sdk.transforms

Class Combine.GloballyAsSingletonView<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.GloballyAsSingletonView<InputT,​OutputT>
extends PTransform<PCollection<InputT>,​PCollectionView<OutputT>>
    Combine.GloballyAsSingletonView<InputT, OutputT> takes a PCollection<InputT> and returns a PCollectionView<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 a value is requested from the view for a window that is not present and insertDefault is true, the result of calling the CombineFn on empty input will returned. If insertDefault is false, an exception will be thrown instead.

    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

      • expand

        public PCollectionView<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>,​PCollectionView<OutputT>>

      • getFanout

        public int getFanout()

      • getInsertDefault

        public boolean getInsertDefault()

      • 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>,​PCollectionView<OutputT>>
        Parameters:
        builder - The builder to populate with display data.
        See Also:
        HasDisplayData