How does R do exact wilcox rank sum tests?

Question

I read the documentation in R for wilcox.test() and want to determine:

1. How R computes wilcox.test()
2. The docs say that when the number of samples is small, it does the test exactly (instead of using a normal approximation) -- what tables does it use to do this exactly?

Answer 1

wilcox.test.default is "hidden" in the stats package's namespace.

That's why you need to do getAnywhere("wilcox.test.default") or stats:::wilcox.test.default to view it.

Answer 2

Package exactRankTests can do exact wilcox rank sum tests.