[
https://issues.apache.org/jira/browse/BEAM-4461?focusedWorklogId=149434&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-149434
]
ASF GitHub Bot logged work on BEAM-4461:
----------------------------------------
Author: ASF GitHub Bot
Created on: 28/Sep/18 19:40
Start Date: 28/Sep/18 19:40
Worklog Time Spent: 10m
Work Description: reuvenlax commented on a change in pull request #6298:
[BEAM-4461] Introduce Group transform.
URL: https://github.com/apache/beam/pull/6298#discussion_r221361037
##########
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:
This is closer to the Dataframes model, which I think is what we should be
aiming at for a programmatic approach. It's also what fits in with Beam, where
aggregations and groupbykey are intimately related. I don't think these
transforms have to match SQL - we already have SQL for that scenario.
The output schema is specified by the aggregateField calls (that's why you
have to specify a field name in those calls).
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Issue Time Tracking
-------------------
Worklog Id: (was: 149434)
Time Spent: 11h 20m (was: 11h 10m)
> 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: 11h 20m
> Remaining Estimate: 0h
>
> e.g. JoinBy(fields). Project, Filter, etc.
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