[R] Exact Permutation test

Stropharia stevenworthington at hotmail.com
Wed Apr 2 23:15:06 CEST 2008


R users,

Is it possible to do 'exact' permutation tests in R? If I run a perm.test or
permutation.test.discrete on a data set that has, for example, 720 possible
permutations, will that test permute ALL of those possible permutations, or
will it just permute 720 random permutations (thus allowing some
possibilities to repeat and some not to be permuted at all)?

I'm a little confused by how to code for a permutation test where I will
have several subsets within the data that need to be maintained, for
example:

Labels: A B C D E F
Codes: 0 0 2 1 1 1

In the above data, if I want to permute all possible combinations of the
'Codes', while maintaining the quantities of zeros, ones and twos in each
permutation, I would compute - 5!/(2!)(1!)(3!) = 10. Is there a way to code
a permutation test so that it will compute all possible combinations like in
the above example, and then dump each permutation into a separate column
vector?

Thanks in advance for any help with this. Much appreciated.

Steve

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