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https://issues.apache.org/jira/browse/DATAFU-3?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13871705#comment-13871705
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Xiangrui Meng commented on DATAFU-3:
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Hi Josh,
Just want to mention that there is a UDF pair in DataFu that implements a
scalable algorithm I developed for simple random sampling with replacement.
Please check the javadoc at
https://github.com/linkedin/datafu/blob/master/src/java/datafu/pig/sampling/SimpleRandomSampleWithReplacementVote.java
It guarantees the correct sample size with probability at least 99.99%, while
the running time is O(n + s log(s)) and the size of the intermediate storage is
O(s log(s)), where n is the size of the population and s is the desired sample
size.
Best,
Xiangrui
> Bootstrap sum UDF
> -----------------
>
> Key: DATAFU-3
> URL: https://issues.apache.org/jira/browse/DATAFU-3
> Project: DataFu
> Issue Type: Bug
> Reporter: Josh Wills
>
> There was a Sawzall table called bootstrapsum that I used to find handy for
> some of the analysis work I did at teh goog:
> http://szl.googlecode.com/svn/trunk/src/emitters/szlbootstrapsum.cc
> It would be nice to have it back again in the Hadoop ecosystem. There was a
> good blog post about the utility of Poisson bootstraps for random forests
> here:
> http://blog.cloudera.com/blog/2013/02/how-to-resample-from-a-large-data-set-in-parallel-with-r-on-hadoop/
> ...but it's useful in all sorts of nerdy stats contexts (e.g., computing
> confidence intervals for experiments.) I'm open to the particular structure
> of the function; it could either have:
> 1) A constructor that took in the number of bootstrap samples to create and
> then a call() method that took in a counting variable and a weighting
> variable, or
> 2) Three args to the call method (num samples, counting variable, and
> weighting variable, in some order.)
> The return type would be a bag of tuples, (index: int, sum: T) where the type
> of the sum would depend on the input type of the counting variable. index = 0
> would always be the actual sum computed, while the rest of the indices would
> be numbered 1..numSamples for each of the different bootstrap samples.
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