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| <html> |
| <h2>Combine - Combine PerKey</h2> |
| <p> |
| After creating a keyed PCollection (for example, by using a GroupByKey transform), a common |
| pattern is to combine the collection of values associated with each key into a single, merged |
| value. This pattern of a GroupByKey followed by merging the collection of values is equivalent to |
| Combine PerKey transform. The combine function you supply to Combine PerKey must be an associative |
| reduction function or a subclass of CombineFn. |
| </p> |
| <p> |
| <b>Kata:</b> Implement the sum of scores per player using |
| <a href="https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/transforms/CombineFnBase.GlobalCombineFn.html"> |
| Combine.perKey</a>. |
| </p> |
| <br> |
| <div class="hint"> |
| Use <a href="https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/transforms/CombineFnBase.GlobalCombineFn.html"> |
| Combine.perKey(GlobalCombineFn)</a>. |
| </div> |
| <div class="hint"> |
| Extend the |
| <a href="https://beam.apache.org/releases/javadoc/current/org/apache/beam/sdk/transforms/Combine.BinaryCombineFn.html"> |
| Combine.BinaryCombineFn</a> class that counts the sum of the number. |
| </div> |
| <div class="hint"> |
| Refer to the Beam Programming Guide |
| <a href="https://beam.apache.org/documentation/programming-guide/#combining-values-in-a-keyed-pcollection"> |
| "Combining values in a keyed PCollection"</a> section for more information. |
| </div> |
| </html> |