org.apache.beam.sdk.transforms

Class WithKeys<K,V>

java.lang.Object

org.apache.beam.sdk.transforms.PTransform<PCollection<V>,PCollection<KV<K,V>>>

org.apache.beam.sdk.transforms.WithKeys<K,V>

Type Parameters:

K - the type of the keys in the output PCollection

V - the type of the elements in the input PCollection and the values in the output PCollection

All Implemented Interfaces:

java.io.Serializable, HasDisplayData

public class WithKeys<K,V>
extends PTransform<PCollection<V>,PCollection<KV<K,V>>>

WithKeys<K, V> takes a PCollection<V>, and either a constant key of type K or a function from V to K, and returns a PCollection<KV<K, V>>, where each of the values in the input PCollection has been paired with either the constant key or a key computed from the value.

Example of use:

 PCollection<String> words = ...;
 PCollection<KV<Integer, String>> lengthsToWords =
     words.apply(WithKeys.of(new SerializableFunction<String, Integer>() {
         public Integer apply(String s) { return s.length(); } }));
 

Each output element has the same timestamp and is in the same windows as its corresponding input element, and the output PCollection has the same WindowFn associated with it as the input.

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<KV<K,V>>	expand(PCollection<V> in) Override this method to specify how this PTransform should be expanded on the given InputT.
static <K,V> WithKeys<K,V>	of(K key) Returns a PTransform that takes a PCollection<V> and returns a PCollection<KV<K, V>>, where each of the values in the input PCollection has been paired with the given key.
static <K,V> WithKeys<K,V>	of(SerializableFunction<V,K> fn) Returns a PTransform that takes a PCollection<V> and returns a PCollection<KV<K, V>>, where each of the values in the input PCollection has been paired with a key computed from the value by invoking the given SerializableFunction.
WithKeys<K,V>	withKeyType(TypeDescriptor<K> keyType) Return a WithKeys that is like this one with the specified key type descriptor.

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

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

Methods inherited from class java.lang.Object

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

Method Detail

of

public static <K,V> WithKeys<K,V> of(SerializableFunction<V,K> fn)

Returns a PTransform that takes a PCollection<V> and returns a PCollection<KV<K, V>>, where each of the values in the input PCollection has been paired with a key computed from the value by invoking the given SerializableFunction.

If using a lambda in Java 8, withKeyType(TypeDescriptor) must be called on the result PTransform.

of

public static <K,V> WithKeys<K,V> of(@Nullable
                                     K key)

Returns a PTransform that takes a PCollection<V> and returns a PCollection<KV<K, V>>, where each of the values in the input PCollection has been paired with the given key.

withKeyType

public WithKeys<K,V> withKeyType(TypeDescriptor<K> keyType)

Return a WithKeys that is like this one with the specified key type descriptor.

For use with lambdas in Java 8, either this method must be called with an appropriate type descriptor or PCollection.setCoder(Coder) must be called on the output PCollection.

expand

public PCollection<KV<K,V>> expand(PCollection<V> in)

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<V>,PCollection<KV<K,V>>>