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https://issues.apache.org/jira/browse/BEAM-10551?focusedWorklogId=461771&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-461771
]
ASF GitHub Bot logged work on BEAM-10551:
-----------------------------------------
Author: ASF GitHub Bot
Created on: 21/Jul/20 22:53
Start Date: 21/Jul/20 22:53
Worklog Time Spent: 10m
Work Description: amaliujia commented on a change in pull request #12313:
URL: https://github.com/apache/beam/pull/12313#discussion_r458434671
##########
File path:
sdks/java/extensions/sql/src/main/java/org/apache/beam/sdk/extensions/sql/impl/transform/BeamBuiltinAnalyticFunctions.java
##########
@@ -42,4 +44,77 @@
throw new UnsupportedOperationException(
String.format("Analytics Function [%s] is not supported",
functionName));
}
+
+ public static <T> Combine.CombineFn<T, ?, T> navigationFirstValue() {
+ return new FirstValueCombineFn();
+ }
+
+ public static <T> Combine.CombineFn<T, ?, T> navigationLastValue() {
+ return new LastValueCombineFn();
+ }
+
+ private static class FirstValueCombineFn<T> extends Combine.CombineFn<T,
Optional<T>, T> {
+ private FirstValueCombineFn() {}
+
+ @Override
+ public Optional<T> createAccumulator() {
+ return Optional.empty();
+ }
+
+ @Override
+ public Optional<T> addInput(Optional<T> accumulator, T input) {
+ Optional<T> r = accumulator;
+ if (!accumulator.isPresent()) {
+ r = Optional.of(input);
+ }
+ return r;
+ }
+
+ @Override
+ public Optional<T> mergeAccumulators(Iterable<Optional<T>> accumulators) {
+ Optional<T> r = Optional.empty();
+ for (Optional<T> ac : accumulators) {
+ if (!r.isPresent() && ac.isPresent()) {
+ r = ac;
Review comment:
Ah I see. Yes it's actually called sequentially on the sorted input.
I think you can through an
[UnsupportedOperationException](https://docs.oracle.com/javase/7/docs/api/java/lang/UnsupportedOperationException.html)
in `mergeAccumulators ` since you will not call mergeAccumulators.
And in the future if there is usage to call `mergeAccumulators`, the
exception will be hit and people will know they need to implement it.
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Issue Time Tracking
-------------------
Worklog Id: (was: 461771)
Time Spent: 20m (was: 10m)
> Implement Navigation Functions FIRST_VALUE and LAST_VALUE
> ---------------------------------------------------------
>
> Key: BEAM-10551
> URL: https://issues.apache.org/jira/browse/BEAM-10551
> Project: Beam
> Issue Type: New Feature
> Components: sdk-java-core
> Reporter: John Mora
> Priority: P2
> Time Spent: 20m
> Remaining Estimate: 0h
>
> Specs:
>
> [https://cloud.google.com/bigquery/docs/reference/standard-sql/navigation_functions#first_value]
>
> [https://cloud.google.com/bigquery/docs/reference/standard-sql/navigation_functions#last_value]
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