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https://issues.apache.org/jira/browse/FLINK-8914?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16623711#comment-16623711
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ASF GitHub Bot commented on FLINK-8914:
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dawidwys commented on issue #6124: [FLINK-8914][CEP]Fix wrong semantic when
greedy pattern is the head of the pattern
URL: https://github.com/apache/flink/pull/6124#issuecomment-423553722
Hi @Aitozi. As I described previously, this case should be handled with
greedy and proper `AfterMatchSkip` strategy. Would you be ok with closing this
PR?
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> CEP's greedy() modifier doesn't work
> ------------------------------------
>
> Key: FLINK-8914
> URL: https://issues.apache.org/jira/browse/FLINK-8914
> Project: Flink
> Issue Type: Bug
> Components: CEP
> Affects Versions: 1.4.0, 1.4.1
> Reporter: David Anderson
> Assignee: aitozi
> Priority: Major
> Labels: pull-request-available
>
> When applied to the first or last component of a CEP Pattern, greedy()
> doesn't work correctly. Here's an example:
> {code:java}
> package com.dataartisans.flinktraining.exercises.datastream_java.cep;
> import org.apache.flink.cep.CEP;
> import org.apache.flink.cep.PatternSelectFunction;
> import org.apache.flink.cep.PatternStream;
> import org.apache.flink.cep.pattern.Pattern;
> import org.apache.flink.cep.pattern.conditions.SimpleCondition;
> import org.apache.flink.streaming.api.datastream.DataStream;
> import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
> import java.util.List;
> import java.util.Map;
> public class RunLength {
> public static void main(String[] args) throws Exception {
> StreamExecutionEnvironment env =
> StreamExecutionEnvironment.getExecutionEnvironment();
> env.setParallelism(1);
> DataStream<Integer> input = env.fromElements(1, 1, 1, 1, 1, 0, 1, 1, 1,
> 0);
> Pattern<Integer, ?> onesThenZero = Pattern.<Integer>begin("ones")
> .where(new SimpleCondition<Integer>() {
> @Override
> public boolean filter(Integer value) throws Exception {
> return value == 1;
> }
> })
> .oneOrMore()
> .greedy()
> .consecutive()
> .next("zero")
> .where(new SimpleCondition<Integer>() {
> @Override
> public boolean filter(Integer value) throws Exception {
> return value == 0;
> }
> });
> PatternStream<Integer> patternStream = CEP.pattern(input, onesThenZero);
> // Expected: 5 3
> // Actual: 5 4 3 2 1 3 2 1
> patternStream.select(new LengthOfRun()).print();
> env.execute();
> }
> public static class LengthOfRun implements PatternSelectFunction<Integer,
> Integer> {
> public Integer select(Map<String, List<Integer>> pattern) {
> return pattern.get("ones").size();
> }
> }
> }
> {code}
> The only workaround for now seems to be to rewrite the pattern so that
> greedy() isn't needed – i.e. by bracketing the greedy section with a prefix
> and suffix that both have to be matched.
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