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:

java.io.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:

Serialized Form

Field Summary

Fields inherited from class org.apache.beam.sdk.transforms.PTransform

name

Method Summary

Modifier and Type	Method and Description
PCollection<OutputT>	expand(PCollection<? extends InputT> input) Override this method to specify how this PTransform should be expanded on the given InputT.
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(SerializableFunction).
void	populateDisplayData(DisplayData.Builder builder) Register display data for the given transform or component.
<NewInputT> MapElements<NewInputT,OutputT>	via(Contextful<Contextful.Fn<NewInputT,OutputT>> fn) Like via(SerializableFunction), but supports access to context, such as side inputs.
<NewInputT> MapElements<NewInputT,OutputT>	via(SerializableFunction<NewInputT,OutputT> fn) For a SerializableFunction<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.
static <InputT,OutputT> MapElements<InputT,OutputT>	via(SimpleFunction<InputT,OutputT> fn) For a SimpleFunction<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.

Methods inherited from class org.apache.beam.sdk.transforms.PTransform

compose, getAdditionalInputs, getDefaultOutputCoder, getDefaultOutputCoder, getDefaultOutputCoder, getKindString, getName, toString, validate

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Method Detail

via

public static <InputT,OutputT> MapElements<InputT,OutputT> via(SimpleFunction<InputT,OutputT> fn)

For a SimpleFunction<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.

This overload is intended primarily for use in Java 7. In Java 8, the overload via(SerializableFunction) supports use of lambda for greater concision.

Example of use in Java 7:

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

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(SerializableFunction).

via

public <NewInputT> MapElements<NewInputT,OutputT> via(SerializableFunction<NewInputT,OutputT> fn)

For a SerializableFunction<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 of use in Java 8:

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

In Java 7, the overload via(SimpleFunction) is more concise as the output type descriptor need not be provided.

via

@Experimental(value=CONTEXTFUL)
public <NewInputT> MapElements<NewInputT,OutputT> via(Contextful<Contextful.Fn<NewInputT,OutputT>> fn)

Like via(SerializableFunction), 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:

HasDisplayData