scikit-learn/scikit-learn — pull request #961 by robertlayton (2012-07-18 00:05:13+00:00)
Title: WIP: Silhouette Coefficient returns 'nan' when a cluster has 1 sample (issue #960)

The Silhouette Coefficient returns a nan value when any cluster (or class) has just 1 value.
This corresponds to issue #960.

I have written a test, based on @aflag's code, to repeat this behaviour.

**TODO**
* Determine the best way to fix this code
* Do that