Matthew Hayes created DATAFU-2:
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Summary: UDFs for entropy and weighted sampling algorithms
Key: DATAFU-2
URL: https://issues.apache.org/jira/browse/DATAFU-2
Project: DataFu
Issue Type: Task
Reporter: Matthew Hayes
Jian Wang has suggested that we add UDFs for entropy and weighted random
sampling and has implementations for each of these ready.
In his words:
"In the real world, there are occasions we need to calculate the entropy of
discrete random variables, for instance, to calculate the mutual information
between variable X and Y using its entropy-based formula(mutual information
calculation could be found at
http://en.wikipedia.org/wiki/Mutual_information#Relation_to_other_quantities).
Would suggest to implement a UDF to calculate the entropy of given input
samples, following the definition at
http://en.wikipedia.org/wiki/Entropy_%28information_theory%29
This is the reference paper I use to learn about the weighted sampleing
algorithm: http://utopia.duth.gr/~pefraimi/research/data/2007EncOfAlg.pdf
The present WeightedSample.java implements the Algorithm D.
We may try Algorithm A, A-res and A-expJ since they could be used in a data
stream and distributed environment. These algorithms could be implemented based
on ReservoirSample.java(inherit from this class?) since they also need a
reservior to store the selected items."
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