GitHub user actuaryzhang opened a pull request:
https://github.com/apache/spark/pull/17879
[SPARK-20619][ML]StringIndexer supports multiple ways of label ordering
## What changes were proposed in this pull request?
StringIndexer maps labels to numbers according to the descending order of
label frequency. Other types of ordering (e.g., alphabetical) may be needed in
feature ETL, for example, this will affect the result in one-hot encoding. The
PR proposes to support other ordering method including alphabetic order and
ascending order of label frequency. We add a parameter `stringOrderType` to
control how string is ordered which supports four options:
- 'freq_desc': descending order by label frequency (most frequent label
assigned 0)
- 'freq_asc': ascending order by label frequency (least frequent label
assigned 0)
- 'alphabet_desc': descending alphabetical order
- 'alphabet_asc': ascending alphabetical order
The default is still descending order of label frequency, so there should
be no impact to existing programs.
## How was this patch tested?
new test
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/actuaryzhang/spark stringIndexer
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/17879.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 #17879
----
commit ffd0cfc755586402c0f22e4458149eed16f98010
Author: Wayne Zhang <[email protected]>
Date: 2017-05-06T06:54:41Z
StringIndexer supports multiple ways of label ordering
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