https://github.com/cran/pracma
Tip revision: 392ae21a013fb3f518e8f9eb8efb458a55a2eca2 authored by HwB on 09 April 2011, 00:00:00 UTC
version 0.3-0
version 0.3-0
Tip revision: 392ae21
perms.R
##
## p e r m s . R Permutations
##
perms <- function(a) {
n <- length(a)
if (length(a) == 0) return(c())
else if (n <= 1) return(matrix(a, 1, 1))
q <- perms(1:(n-1)) # recursive call
m <- nrow(q)
P <- matrix(0, n*m, n)
P[1:m, ] <- cbind(matrix(n, m, 1), q)
for (i in (n-1):1) {
t <- q
t[t == i] <- n
P[(m*(n-i)+1):(m*(n-i+1)), ] <- cbind(i*matrix(1, m, 1), t)
}
b <- a[c(P)]
dim(b) <- dim(P)
return(b)
}
randperm <- function(a) {
n <- length(a)
if (n == 0) return(c())
else if (n <= 1) return(a)
m <- sample(1:n, size = n, replace = FALSE)
return(a[m])
}