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.
   */
  
  package org.apache.beam.learning.katas.coretransforms.flatten;
  
  // beam-playground:
  //   name: Flatten
  //   description: Task from katas that merges two PCollections of words into a single PCollection.
  //   multifile: false
  //   context_line: 47
  //   categories:
  //     - Combiners
  //     - Flatten
  //     - Core Transforms
  //   complexity: BASIC
  //   tags:
  //     - transforms
  //     - join
  //     - strings
  
  import org.apache.beam.learning.katas.util.Log;
  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.Create;
  import org.apache.beam.sdk.transforms.Flatten;
  import org.apache.beam.sdk.values.PCollection;
  import org.apache.beam.sdk.values.PCollectionList;
  
  public class Task {
  
    public static void main(String[] args) {
      PipelineOptions options = PipelineOptionsFactory.fromArgs(args).create();
      Pipeline pipeline = Pipeline.create(options);
  
      PCollection<String> wordsStartingWithA =
          pipeline.apply("Words starting with A",
              Create.of("apple", "ant", "arrow")
          );
  
      PCollection<String> wordsStartingWithB =
          pipeline.apply("Words starting with B",
              Create.of("ball", "book", "bow")
          );
  
      PCollection<String> output = applyTransform(wordsStartingWithA, wordsStartingWithB);
  
      output.apply(Log.ofElements());
  
      pipeline.run();
    }
  
    static PCollection<String> applyTransform(
        PCollection<String> words1, PCollection<String> words2) {
  
      return PCollectionList.of(words1).and(words2)
          .apply(Flatten.pCollections());
    }
  
  }