[
https://issues.apache.org/jira/browse/BEAM-4461?focusedWorklogId=147562&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-147562
]
ASF GitHub Bot logged work on BEAM-4461:
----------------------------------------
Author: ASF GitHub Bot
Created on: 25/Sep/18 13:37
Start Date: 25/Sep/18 13:37
Worklog Time Spent: 10m
Work Description: akedin commented on a change in pull request #6298:
[BEAM-4461] Introduce Group transform.
URL: https://github.com/apache/beam/pull/6298#discussion_r220191831
##########
File path:
sdks/java/core/src/main/java/org/apache/beam/sdk/schemas/transforms/Group.java
##########
@@ -0,0 +1,684 @@
+/*
+ * 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.sdk.schemas.transforms;
+
+import java.util.List;
+import javax.annotation.Nullable;
+import org.apache.beam.sdk.annotations.Experimental;
+import org.apache.beam.sdk.annotations.Experimental.Kind;
+import org.apache.beam.sdk.coders.KvCoder;
+import org.apache.beam.sdk.schemas.FieldAccessDescriptor;
+import org.apache.beam.sdk.schemas.Schema;
+import org.apache.beam.sdk.schemas.Schema.Field;
+import org.apache.beam.sdk.schemas.SchemaCoder;
+import org.apache.beam.sdk.transforms.Combine;
+import org.apache.beam.sdk.transforms.Combine.CombineFn;
+import org.apache.beam.sdk.transforms.DoFn;
+import org.apache.beam.sdk.transforms.GroupByKey;
+import org.apache.beam.sdk.transforms.PTransform;
+import org.apache.beam.sdk.transforms.ParDo;
+import org.apache.beam.sdk.transforms.Values;
+import org.apache.beam.sdk.transforms.WithKeys;
+import org.apache.beam.sdk.values.KV;
+import org.apache.beam.sdk.values.PCollection;
+import org.apache.beam.sdk.values.Row;
+
+/**
+ * A generic grouping transform for schema {@link PCollection}s.
+ *
+ * <p>When used without a combiner, this transforms simply acts as a {@link
GroupByKey} but without
+ * the need for the user to explicitly extract the keys. For example, consider
the following input
+ * type:
+ *
+ * <pre>{@code
+ * {@literal @DefaultSchema(JavaFieldSchema.class)}
+ * public class UserPurchase {
+ * public String userId;
+ * public String country;
+ * public long cost;
+ * public double transactionDuration;
+ * }
+ *
+ * {@literal PCollection<UserPurchase>} purchases = readUserPurchases();
+ * }</pre>
+ *
+ * <p>You can group all purchases by user and country as follows:
+ *
+ * <pre>{@code
+ * {@literal @DefaultSchema(JavaFieldSchema.class)}
+ * {@literal PCollection<KV<Row, Iterable<UserPurchase>>} byUser =
+ * purchases.apply(Group.byFieldNames("userId', "country"));
+ * }</pre>
+ *
+ * <p>However often an aggregation of some form is desired. The builder
methods inside the Group
+ * class allows building up separate aggregations for every field (or set of
fields) on the input
+ * schema, and generating an output schema based on these aggregations. For
example:
+ *
+ * <pre>{@code
+ * {@literal PCollection<KV<Row, Row>>} aggregated = purchases
+ * .apply(Group.byFieldNames("userId', "country")
+ * .aggregateField("cost", Sum.ofLongs(), "total_cost")
Review comment:
I think the syntax is a bit confusing. It mixes up SQL-like `GROUP BY` with
Beam's `GroupByKey`, so for me it takes a second to figure out what this
translates to. E.g. if I read this coming from SQL, it's unclear why I am
grouping by `userId` and `country` but then aggregating only `cost`, but not
grouping by `cost`.
It's also unclear what the output schema here is. Is it only the fields in
the `Group.`? How does it work with `Select`?
Would it be better to follow SQL-like approach? I.e. add aggregations in
`Select` and use `Group` to only specify the keys?
----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on GitHub and use the
URL above to go to the specific comment.
For queries about this service, please contact Infrastructure at:
[email protected]
Issue Time Tracking
-------------------
Worklog Id: (was: 147562)
Time Spent: 10h 50m (was: 10h 40m)
> Create a library of useful transforms that use schemas
> ------------------------------------------------------
>
> Key: BEAM-4461
> URL: https://issues.apache.org/jira/browse/BEAM-4461
> Project: Beam
> Issue Type: Sub-task
> Components: sdk-java-core
> Reporter: Reuven Lax
> Assignee: Reuven Lax
> Priority: Major
> Time Spent: 10h 50m
> Remaining Estimate: 0h
>
> e.g. JoinBy(fields). Project, Filter, etc.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
