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https://issues.apache.org/jira/browse/SPARK-3250?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14140897#comment-14140897
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Apache Spark commented on SPARK-3250:
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User 'erikerlandson' has created a pull request for this issue:
https://github.com/apache/spark/pull/2455

> More Efficient Sampling
> -----------------------
>
>                 Key: SPARK-3250
>                 URL: https://issues.apache.org/jira/browse/SPARK-3250
>             Project: Spark
>          Issue Type: Improvement
>          Components: Spark Core
>            Reporter: RJ Nowling
>
> Sampling, as currently implemented in Spark, is an O\(n\) operation.  A 
> number of stochastic algorithms achieve speed ups by exploiting O\(k\) 
> sampling, where k is the number of data points to sample.  Examples of such 
> algorithms include KMeans MiniBatch (SPARK-2308) and Stochastic Gradient 
> Descent with mini batching.
> More efficient sampling may be achievable by packing partitions with an 
> ArrayBuffer or other data structure supporting random access.  Since many of 
> these stochastic algorithms perform repeated rounds of sampling, it may be 
> feasible to perform a transformation to change the backing data structure 
> followed by multiple rounds of sampling.



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