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2018 Mar 30
0
getting all circular arrangements without accounting for order
New function below is a bit faster due to more efficent memory handling. for-loop FTW! directionless_circular_permutations2 <- function( n ) { n1 <- n - 1L v <- seq.int( n1 ) ix <- combinations( n1, 2L ) jx <- permutations( n-3L, n-3L ) jxrows <- nrow( jx ) jxoffsets <- seq.int( jxrows ) result <- matrix( n, nrow = factorial( n1 )/2L, ncol = n ) k <- seq( 2L, n - 2L ) for ( i in seq.int( nrow( ix ) ) ) { result[ ( i - 1L ) * jxrows + jxoffsets, k ] <- matrix( v[ -ix[ i, ] ][ jx ], nrow = jxrows )...
2018 Mar 30
2
getting all circular arrangements without accounting for order
Jeff, I wanted to let you know that your function is faster than generating the directional circular permutations and weeding. Here is the time for n = 10. I compared with just doing the permutations, there is no point in proceeding further with the weeding since it is slower at the start itself. system.time(directionless_circular_permutations(10)) user system elapsed 1.576 0.000