content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you under the Apache License, Version 2.0 (the
   * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  import org.apache.beam.sdk.Pipeline;
  import org.apache.beam.sdk.options.PipelineOptions;
  import org.apache.beam.sdk.options.PipelineOptionsFactory;
  import org.apache.beam.sdk.transforms.Combine;
  import org.apache.beam.sdk.transforms.Create;
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.ParDo;
  import org.apache.beam.sdk.transforms.Sum;
  import org.apache.beam.sdk.values.KV;
  import org.apache.beam.sdk.values.PCollection;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  // beam-playground:
  //   name: CombinePerKey
  //   description: Demonstration of Combine.perKey transform usage.
  //   multifile: false
  //   default_example: false
  //   context_line: 48
  //   categories:
  //     - Core Transforms
  //   complexity: BASIC
  //   tags:
  //     - transforms
  //     - numbers
  //     - distinct
  
  public class CombinePerKeyExample {
    public static void main(String[] args) {
      PipelineOptions options = PipelineOptionsFactory.create();
      Pipeline pipeline = Pipeline.create(options);
  
      // [START main_section]
      // PCollection is grouped by key and the Double values associated with each key
      // are combined into a Double.
      PCollection<KV<String, Double>> salesRecords =
          pipeline.apply(
              Create.of(
                  KV.of("Apples", 2.0),
                  KV.of("Apples", 3.0),
                  KV.of("Apples", 5.0),
                  KV.of("Oranges", 4.0),
                  KV.of("Oranges", 8.0)));
      PCollection<KV<String, Double>> totalSalesPerPerson =
          salesRecords.apply(Combine.perKey(Sum.ofDoubles()));
      // [END main_section]
      // Log values
      totalSalesPerPerson.apply(
          ParDo.of(new LogOutput<>("PCollection numbers after Combine.perKey transform: ")));
      pipeline.run();
    }
  
    static class LogOutput<T> extends DoFn<T, T> {
      private static final Logger LOG = LoggerFactory.getLogger(LogOutput.class);
      private final String prefix;
  
      public LogOutput(String prefix) {
        this.prefix = prefix;
      }
  
      @ProcessElement
      public void processElement(ProcessContext c) throws Exception {
        LOG.info(prefix + c.element());
        c.output(c.element());
      }
    }
  }
  