Get the nth Permutation Vector by Periodic Placement
numperm implicitly numbers all permutations of length olength, returning the permnumth of these.
numperm(olength, permnum)
olength |
The number of items to permute |
permnum |
The number of the permutation to use (in |
The n! permutations on n items can be deterministically ordered via a factorization process in which there are n slots for the first element, n-1 for the second, and n-i for the ith. This fact is quite handy if you want to visit each permutation in turn, or if you wish to sample without replacement from the set of permutations on some number of elements: one just enumerates or samples from the integers on [1,n!], and then find the associated permutation. numperm performs exactly this last operation, returning the permnumth permutation on olength items.
A permutation vector
Permutation search is central to the estimation of structural distances, correlations, and covariances on partially labeled graphs. numperm is hence used by structdist, gscor, gscov, etc.
Carter T. Butts buttsc@uci.edu
#Draw a graph g<-rgraph(5) #Permute the rows and columns p.1<-numperm(5,1) p.2<-numperm(5,2) p.3<-numperm(5,3) g[p.1,p.1] g[p.2,p.2] g[p.3,p.3]
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