GitHub user davies opened a pull request:
https://github.com/apache/spark/pull/2142
[SPARK-2871] [PySpark] add countApproxDistinct() API
RDD.countApproxDistinct(relativeSD=0.05):
:: Experimental ::
Return approximate number of distinct elements in the RDD.
The algorithm used is based on streamlib's implementation of
"HyperLogLog in Practice: Algorithmic Engineering of a State
of The Art Cardinality Estimation Algorithm", available
<a href="http://dx.doi.org/10.1145/2452376.2452456";>here</a>.
This support all the types of objects, which is supported by
Pyrolite, nearly all builtin types.
@param relativeSD Relative accuracy. Smaller values create
counters that require more space.
It must be greater than 0.000017.
>>> n = sc.parallelize(range(1000)).map(str).countApproxDistinct()
>>> 950 < n < 1050
True
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/davies/spark countApproxDistinct
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/2142.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #2142
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commit e97e342dac1cbbad2e424a39159a6c7f3fa63bf4
Author: Davies Liu <[email protected]>
Date: 2014-08-26T18:49:34Z
add countApproxDistinct()
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