Package org.apache.beam.sdk.transforms

Class MapKeys<K1,K2,V>

java.lang.Object
org.apache.beam.sdk.transforms.PTransform<PCollection<KV<K1,V>>,PCollection<KV<K2,V>>>
org.apache.beam.sdk.transforms.MapKeys<K1,K2,V>
Type Parameters:
K1 - the type of the keys in the input PCollection
K2 - the type of the keys in the output PCollection
All Implemented Interfaces:
Serializable, HasDisplayData
public class MapKeys<K1,K2,V> extends PTransform<PCollection<KV<K1,V>>,PCollection<KV<K2,V>>>
MapKeys maps a SerializableFunction<K1,K2> over keys of a PCollection<KV<K1,V>> and returns a PCollection<KV<K2, V>>.

Example of use: 


 PCollection<KV<Integer, String>> input = ...;
 PCollection<KV<Double, String> output =
      input.apply(MapKeys.into(TypeDescriptors.doubles()).via(Integer::doubleValue));

See also MapValues.

See Also:

  • Method Details

    • via

      public <NewValueT, NewKeyT> MapKeys<NewKeyT,K2,NewValueT> via(SerializableFunction<NewKeyT,K2> fn)
      Returns a MapKeys<K1, K2, V> PTransform for a ProcessFunction<NewK1, K2> with predefined outputType.
      Type Parameters:
      NewValueT - the type of the values in the input and output PCollections
      NewKeyT - the type of the keys in the input PCollection

    • into

      public static <K2> MapKeys<?,K2,?> into(TypeDescriptor<K2> outputType)
      Returns a new MapKeys transform with the given type descriptor for the output type, but the mapping function yet to be specified using via(SerializableFunction).

    • exceptionsInto

      @RequiresNonNull("fn") public <FailureT> org.apache.beam.sdk.transforms.SimpleMapWithFailures<KV<K1,V>,KV<K2,V>,FailureT> exceptionsInto(TypeDescriptor<FailureT> failureTypeDescriptor)
      Returns a new SimpleMapWithFailures 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 SimpleMapWithFailures.exceptionsVia(ProcessFunction).

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

      Example usage: 

      
 Result<PCollection<KV<Integer, String>>, String> result =
         input.apply(
             MapKeys.into(TypeDescriptors.integers())
                 .<String, String>via(word -> 1 / word.length)  // Could throw ArithmeticException
                 .exceptionsInto(TypeDescriptors.strings())
                 .exceptionsVia(ee -> ee.exception().getMessage()));
 PCollection<KV<Integer, String>> output = result.output();
 PCollection<String> failures = result.failures();

    • exceptionsVia

      @RequiresNonNull("fn") public <FailureT> org.apache.beam.sdk.transforms.SimpleMapWithFailures<KV<K1,V>,KV<K2,V>,FailureT> exceptionsVia(InferableFunction<WithFailures.ExceptionElement<KV<K1,V>>,FailureT> exceptionHandler)
      Returns a new SimpleMapWithFailures 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<KV<Integer, String>>, String> result =
         input.apply(
             MapKeys.into(TypeDescriptors.integers())
                 .<String, String>via(word -> 1 / word.length)  // Could throw ArithmeticException
                 .exceptionsVia(
                     new InferableFunction<ExceptionElement<KV<String, String>>, String>() {
                       @Override
                       public String apply(ExceptionElement<KV<String, String>> input) {
                         return input.exception().getMessage();
                       }
                     }));
 PCollection<KV<Integer, String>> output = result.output();
 PCollection<String> failures = result.failures();

    • expand

      public PCollection<KV<K2,V>> expand(PCollection<KV<K1,V>> 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<KV<K1,V>>,PCollection<KV<K2,V>>>