histogram() UDAF for a numerical column
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Key: HIVE-1397
URL: https://issues.apache.org/jira/browse/HIVE-1397
Project: Hadoop Hive
Issue Type: New Feature
Components: Query Processor
Affects Versions: 0.6.0
Reporter: Mayank Lahiri
Assignee: Mayank Lahiri
Fix For: 0.6.0
A histogram() UDAF to generate an approximate histogram of a numerical (byte,
short, double, long, etc.) column. The result is returned as a map of (x,y)
histogram pairs, and can be plotted in Gnuplot using impulses (for example).
The algorithm is currently adapted from "A streaming parallel decision tree
algorithm" by Ben-Haim and Tom-Tov, JMLR 11 (2010), and uses space proportional
to the number of histogram bins specified. It has no approximation guarantees,
but seems to work well when there is a lot of data and a large number (e.g.
50-100) of histogram bins specified.
A typical call might be:
SELECT histogram(val, 10) FROM some_table;
where the result would be a histogram with 10 bins, returned as a Hive map
object.
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