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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 )
}
result[ , 1L ] <-...
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