R/permutations.R

In HelpersMG: Tools for Environmental Analyses, Ecotoxicology and Various R Functions

.permutations <- function (n, r, v = 1:n, set = TRUE, repeats.allowed = FALSE) 
  
  # code from the package gtools
{
  if (mode(n) != "numeric" || length(n) != 1 || n < 1 || (n%%1) != 
      0) 
    stop("bad value of n")
  if (mode(r) != "numeric" || length(r) != 1 || r < 1 || (r%%1) != 
      0) 
    stop("bad value of r")
  if (!is.atomic(v) || length(v) < n) 
    stop("v is either non-atomic or too short")
  if ((r > n) & repeats.allowed == FALSE) 
    stop("r > n and repeats.allowed=FALSE")
  if (set) {
    v <- unique(sort(v))
    if (length(v) < n) 
      stop("too few different elements")
  }
  v0 <- vector(mode(v), 0)
  if (repeats.allowed) 
    sub <- function(n, r, v) {
      if (r == 1) 
        matrix(v, n, 1)
      else if (n == 1) 
        matrix(v, 1, r)
      else {
        inner <- Recall(n, r - 1, v)
        cbind(rep(v, rep(nrow(inner), n)), matrix(t(inner), 
                                                  ncol = ncol(inner), nrow = nrow(inner) * n, 
                                                  byrow = TRUE))
      }
    }
  else sub <- function(n, r, v) {
    if (r == 1) 
      matrix(v, n, 1)
    else if (n == 1) 
      matrix(v, 1, r)
    else {
      X <- NULL
      for (i in 1:n) X <- rbind(X, cbind(v[i], Recall(n - 
                                                        1, r - 1, v[-i])))
      X
    }
  }
  sub(n, r, v[1:n])
}