scikit-learn/scikit-learn — pull request #1182 by fabianp (2012-09-26 10:27:14+00:00)
Title: Add support for preference contraints in svmlight format.

The preference constrains ("qid" in svmlight parlance) adds
the ability to control which pairs are considered when dealing with
pairwise loss functions (e.g. for SVMrank). It is explained in
http://svmlight.joachims.org/.

In order to preserve API compatibility, I return this information (if
present) as a second column to the y vector.

Added a test and paragraph to the docstring.