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Posted to github@beam.apache.org by GitBox <gi...@apache.org> on 2020/06/09 15:54:23 UTC
[GitHub] [beam] damondouglas commented on a change in pull request #11936: [BEAM-9679] Add CombinePerKey to Core Transforms Go Katas
damondouglas commented on a change in pull request #11936:
URL: https://github.com/apache/beam/pull/11936#discussion_r437054701
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File path: learning/katas/go/Core Transforms/Combine/Combine PerKey/task.md
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+
+# Combine - Combine PerKey
Review comment:
It's this way in both the [Java](https://github.com/apache/beam/blob/master/learning/katas/java/Core%20Transforms/Combine/Combine%20PerKey/task.md) and [Python](https://github.com/apache/beam/blob/master/learning/katas/python/Core%20Transforms/Combine/Combine%20PerKey/task.md) task descriptions. I don't mind deviating so perhaps just "Combine per key" as the header?
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File path: learning/katas/go/Core Transforms/Combine/Combine PerKey/task.md
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+<!--
+ ~ 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.
+ -->
+
+# Combine - Combine PerKey
+
+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.
Review comment:
Apologies, I missed that. Would it be clear if we just remove "or a subclass of CombineFn" such that the full sentence reads: "The combine function you supply to beam.CombinePerKey must be an associative reduction function"?
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