Package org.apache.beam.sdk.transforms

Class MapElements<InputT,OutputT>

java.lang.Object
org.apache.beam.sdk.transforms.PTransform<PCollection<? extends InputT>,PCollection<OutputT>>
org.apache.beam.sdk.transforms.MapElements<InputT,OutputT>
All Implemented Interfaces:
Serializable, HasDisplayData
public class MapElements<InputT,OutputT> extends PTransform<PCollection<? extends InputT>,PCollection<OutputT>>
PTransforms for mapping a simple function over the elements of a PCollection.
See Also:

  • Method Details

    • via

      public static <InputT, OutputT> MapElements<InputT,OutputT> via(InferableFunction<InputT,OutputT> fn)
      For InferableFunction<InputT, OutputT> fn, returns a PTransform that takes an input PCollection<InputT> and returns a PCollection<OutputT> containing fn.apply(v) for every element v in the input.

      InferableFunction has the advantage of providing type descriptor information, but it is generally more convenient to specify output type via into(TypeDescriptor), and provide the mapping as a lambda expression to via(ProcessFunction).

      Example usage: 

      
 PCollection<String> words = ...;
 PCollection<Integer> wordsPerLine = words.apply(MapElements.via(
     new InferableFunction<String, Integer>() {
       public Integer apply(String word) throws Exception {
         return word.length();
       }
     }));

    • via

      public static <InputT, OutputT> MapElements<InputT,OutputT> via(SimpleFunction<InputT,OutputT> fn)
      Binary compatibility adapter for via(InferableFunction).

    • into

      public static <OutputT> MapElements<?,OutputT> into(TypeDescriptor<OutputT> outputType)
      Returns a new MapElements transform with the given type descriptor for the output type, but the mapping function yet to be specified using via(ProcessFunction).

    • via

      public <NewInputT> MapElements<NewInputT,OutputT> via(ProcessFunction<NewInputT,OutputT> fn)
      For a ProcessFunction<InputT, OutputT> fn and output type descriptor, returns a PTransform that takes an input PCollection<InputT> and returns a PCollection<OutputT> containing fn.apply(v) for every element v in the input.

      Example usage: 

      
 PCollection<Integer> wordLengths = words.apply(
     MapElements.into(TypeDescriptors.integers())
                .via((String word) -> word.length()));

    • via

      public <NewInputT> MapElements<NewInputT,OutputT> via(SerializableFunction<NewInputT,OutputT> fn)
      Binary compatibility adapter for via(ProcessFunction).

    • via

      public <NewInputT> MapElements<NewInputT,OutputT> via(Contextful<Contextful.Fn<NewInputT,OutputT>> fn)
      Like via(ProcessFunction), but supports access to context, such as side inputs.

    • expand

      public PCollection<OutputT> expand(PCollection<? extends 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<? extends 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<? extends InputT>,PCollection<OutputT>>
      Parameters:
      builder - The builder to populate with display data.
      See Also:

    • exceptionsInto

      public <NewFailureT> MapElements.MapWithFailures<InputT,OutputT,NewFailureT> exceptionsInto(TypeDescriptor<NewFailureT> failureTypeDescriptor)
      Returns a new MapElements.MapWithFailures transform that catches exceptions raised while mapping elements, with the given type descriptor used for the failure collection but the exception handler yet to be specified using MapElements.MapWithFailures.exceptionsVia(ProcessFunction).

      See WithFailures documentation for usage patterns of the returned WithFailures.Result.

    • exceptionsVia

      public <FailureT> MapElements.MapWithFailures<InputT,OutputT,FailureT> exceptionsVia(InferableFunction<WithFailures.ExceptionElement<InputT>,FailureT> exceptionHandler)
      Returns a new MapElements.MapWithFailures transform that catches exceptions raised while mapping elements, passing the raised exception instance and the input element being processed through the given exceptionHandler and emitting the result to a failure collection.

      This method takes advantage of the type information provided by InferableFunction, meaning that a call to exceptionsInto(TypeDescriptor) may not be necessary.

      See WithFailures documentation for usage patterns of the returned WithFailures.Result.

      Example usage: 

      
 Result<PCollection<String>, String>> result = words.apply(
     MapElements
         .into(TypeDescriptors.integers())
         .via((String word) -> 1 / word.length)  // Could throw ArithmeticException
         .exceptionsVia(new WithFailures.ExceptionAsMapHandler<String>() {}));
 PCollection<Integer> output = result.output();
 PCollection<String> failures = result.failures();