Combine.GloballyAsSingletonView (Google Cloud Dataflow SDK 1.9.1 API)

Google Cloud Dataflow SDK for Java, version 1.9.1

Class Combine.GloballyAsSingletonView<InputT,OutputT>

  • Type Parameters:
    InputT - type of input values
    OutputT - type of output values
    All Implemented Interfaces:
    HasDisplayData, Serializable
    Enclosing class:

    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(<java.lang.Iterable<V>, V>)/Combine.PerKey and Combine.groupedValues(<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