This uses leave-one-out cross validation.
For each row of the training set train, the k nearest
(in Euclidean distance) other training set vectors are found, and the classification
is decided by majority vote, with ties broken at random. If there are ties for the
kth nearest vector, all candidates are included in the vote.
References
Ripley, B. D. (1996)
Pattern Recognition and Neural Networks. Cambridge.
Venables, W. N. and Ripley, B. D. (2002)
Modern Applied Statistics with S. Fourth edition. Springer.