InputT - type of input valuesOutputT - type of output valuespublic 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.
name| Modifier and Type | Method and Description |
|---|---|
PCollectionView<OutputT> |
expand(PCollection<InputT> input)
Override this method to specify how this
PTransform should be expanded
on the given InputT. |
CombineFnBase.GlobalCombineFn<? super InputT,?,OutputT> |
getCombineFn() |
int |
getFanout() |
boolean |
getInsertDefault() |
void |
populateDisplayData(DisplayData.Builder builder)
Register display data for the given transform or component.
|
getAdditionalInputs, getDefaultOutputCoder, getDefaultOutputCoder, getDefaultOutputCoder, getKindString, getName, toString, validatepublic PCollectionView<OutputT> expand(PCollection<InputT> input)
PTransformPTransform 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).
expand in class PTransform<PCollection<InputT>,PCollectionView<OutputT>>public int getFanout()
public boolean getInsertDefault()
public CombineFnBase.GlobalCombineFn<? super InputT,?,OutputT> getCombineFn()
public void populateDisplayData(DisplayData.Builder builder)
PTransformpopulateDisplayData(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.
populateDisplayData in interface HasDisplayDatapopulateDisplayData in class PTransform<PCollection<InputT>,PCollectionView<OutputT>>builder - The builder to populate with display data.HasDisplayData