GitHub user wzhfy opened a pull request:
https://github.com/apache/spark/pull/15443
[SPARK-17881] [SQL] Aggregation function for generating string histograms
## What changes were proposed in this pull request?
This agg function generates equi-width histograms in the form of Map(value:
String, frequency: Long) for string type columns, with a maximum number of
histogram bins. It returns a empty result if the ndv(number of distinct value)
of the column exceeds the maximum number allowed.
## How was this patch tested?
add test cases
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/wzhfy/spark stringHistogram
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/15443.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 #15443
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commit a843920983914de7efd21608b8f0e39c70b210d7
Author: wangzhenhua <[email protected]>
Date: 2016-10-12T01:02:37Z
add agg function to generate string histogram
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