• d(X,Y) = (1/|X|) sum(d(x,Y))
• d(x,Y) = min_y (d(x,y))
• d(x,Y) is the nearest neighbor distance between x and Y.

Compute the average and standard deviation of these things.

Unit tests:

• Interface-level tests:
• Error null datasets
• Error on empty datasets

References: Deb00Fast