[GitHub] [beam] rezarokni commented on a change in pull request #15786: Add gap-filling transform for timeseries

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rezarokni commented on a change in pull request #15786:
URL: https://github.com/apache/beam/pull/15786#discussion_r772555579



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File path: sdks/java/extensions/timeseries/src/main/java/org/apache/beam/sdk/extensions/timeseries/FillGaps.java
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@@ -0,0 +1,532 @@
+/*
+ * 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.extensions.timeseries;
+
+import com.google.auto.value.AutoValue;
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.function.Supplier;
+import javax.annotation.Nullable;
+import org.apache.beam.sdk.coders.Coder;
+import org.apache.beam.sdk.coders.InstantCoder;
+import org.apache.beam.sdk.coders.SortedMapCoder;
+import org.apache.beam.sdk.coders.VarLongCoder;
+import org.apache.beam.sdk.schemas.FieldAccessDescriptor;
+import org.apache.beam.sdk.schemas.transforms.WithKeys;
+import org.apache.beam.sdk.state.StateSpec;
+import org.apache.beam.sdk.state.StateSpecs;
+import org.apache.beam.sdk.state.TimeDomain;
+import org.apache.beam.sdk.state.TimerMap;
+import org.apache.beam.sdk.state.TimerSpec;
+import org.apache.beam.sdk.state.TimerSpecs;
+import org.apache.beam.sdk.state.ValueState;
+import org.apache.beam.sdk.transforms.DoFn;
+import org.apache.beam.sdk.transforms.PTransform;
+import org.apache.beam.sdk.transforms.ParDo;
+import org.apache.beam.sdk.transforms.SerializableBiFunction;
+import org.apache.beam.sdk.transforms.SerializableFunction;
+import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
+import org.apache.beam.sdk.transforms.windowing.FixedWindows;
+import org.apache.beam.sdk.transforms.windowing.GlobalWindows;
+import org.apache.beam.sdk.transforms.windowing.Window;
+import org.apache.beam.sdk.transforms.windowing.WindowFn;
+import org.apache.beam.sdk.values.KV;
+import org.apache.beam.sdk.values.PCollection;
+import org.apache.beam.sdk.values.Row;
+import org.apache.beam.sdk.values.TimestampedValue;
+import org.apache.beam.sdk.values.TimestampedValue.TimestampedValueCoder;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Preconditions;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.collect.Maps;
+import org.joda.time.Duration;
+import org.joda.time.Instant;
+
+/**
+ * Fill gaps in timeseries. Values are expected to have Beam schemas registered.
+ *
+ * <p>This transform views the original PCollection as a collection of timeseries, each with a different key. They
+ * key to be used and the timeseries bucket size are both specified in the {@link #of} creation method. Multiple
+ * fields can be specified for the key - the key extracted will be a composite of all of them. Any elements in the
+ * original {@link PCollection} will appear unchanged in the output PCollection, with timestamp and window unchanged.
+ * Any gaps in timeseries (i.e. buckets with no elements) will be filled in the output PCollection with a single element
+ * (by default the latest element seen or propagated into the previous bucket). The timestamp of the filled element is
+ * the end of the bucket, and the original PCollection's window function is used to assign it to a window.
+ *
+ *
+ * <p>Example usage: the following code views each user,country pair in the input {@link PCollection} as a timeseries

Review comment:
       I believe using bucket is more confusing than windows, windows correctly describes what this is. To make the distinction, you could call it gap-window, or something-window. There are plenty of other API's that define the extraction of an object within a discrete time interval as a window. Moving away from the term window  just to make it distinct from the Beam window, would force users who normally work with timeseries data ( the core use case) to have to get use to new nomenclature just for this api.




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