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https://issues.apache.org/jira/browse/SPARK-23091?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Apache Spark reassigned SPARK-23091:
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Assignee: Apache Spark
> Incorrect unit test for approxQuantile
> --------------------------------------
>
> Key: SPARK-23091
> URL: https://issues.apache.org/jira/browse/SPARK-23091
> Project: Spark
> Issue Type: Improvement
> Components: ML, Tests
> Affects Versions: 2.2.1
> Reporter: Kuang Chen
> Assignee: Apache Spark
> Priority: Minor
>
> Currently, test for `approxQuantile` (quantile estimation algorithm) checks
> whether estimated quantile is within +- 2*`relativeError` from the true
> quantile. See the code below:
> [https://github.com/apache/spark/blob/master/sql/core/src/test/scala/org/apache/spark/sql/DataFrameStatSuite.scala#L157]
> However, based on the original paper by Greenwald and Khanna, the estimated
> quantile is guaranteed to be within +- `relativeError` from the true
> quantile. Using the double "tolerance" is misleading and incorrect, and we
> should fix it.
>
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