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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Work logged] (BEAM-4461) Create a library of useful transforms that use schemas
Date Tue, 25 Sep 2018 13:38:00 GMT

     [ https://issues.apache.org/jira/browse/BEAM-4461?focusedWorklogId=147564&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-147564
]

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_r220193157
 
 

 ##########
 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")
+ *          .aggregateField("cost", Top.<Long>largestLongsFn(10), "top_purchases")
+ *          .aggregateField("cost", ApproximateQuantilesCombineFn.create(21),
+ *            Field.of("transactionDurations", FieldType.array(FieldType.INT64)));
+ * }</pre>
+ *
+ * <p>The result will be a new row schema containing the fields total_cost, top_purchases,
and
+ * transactionDurations, containing the sum of all purchases costs (for that user and country),
the
+ * top ten purchases, and a histogram of transaction durations.
+ *
+ * <p>Note that usually the field type can be automatically inferred from the {@link
CombineFn}
+ * passed in. However sometimes it cannot be inferred, due to Java type erasure, in which
case a
+ * {@link Field} object containing the field type must be passed in. This is currently the
case for
+ * ApproximateQuantilesCombineFn in the above example.
+ */
+@Experimental(Kind.SCHEMAS)
+public class Group {
+  /**
+   * Returns a transform that groups all elements in the input {@link PCollection}. The returned
+   * transform contains further builder methods to control how the grouping is done.
+   */
+  public static <T> Global<T> globally() {
+    return new Global<>();
+  }
+
+  /**
+   * Returns a transform that groups all elements in the input {@link PCollection} keyed
by the list
+   * of fields specified. The output of this transform will be a {@link KV} keyed by a {@link
Row}
+   * containing the specified extracted fields. The returned transform contains further builder
+   * methods to control how the grouping is done.
+   */
+  public static <T> ByFields<T> byFieldNames(String... fieldNames) {
 
 Review comment:
   I think it needs an example here, the pseudocode of equivalent `GBK`

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Issue Time Tracking
-------------------

    Worklog Id:     (was: 147564)
    Time Spent: 11h  (was: 10h 50m)

> 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
>  Remaining Estimate: 0h
>
> e.g. JoinBy(fields). Project, Filter, etc.



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