R: Inverse Permutation Vector

invPerm {Matrix}

R Documentation

Inverse Permutation Vector

Description

From a permutation vector p, compute its inverse permutation vector.

Usage

invPerm(p, zero.p = FALSE, zero.res = FALSE)

Arguments

`p`	an integer vector of length, say, `n`.
`zero.p`	logical indicating if `p` contains values `0:(n-1)` or rather (by default, `zero.p = FALSE`) `1:n`.
`zero.res`	logical indicating if the result should contain values `0:(n-1)` or rather (by default, `zero.res = FALSE`) `1:n`.

Value

an integer vector of the same length (n) as p. By default, (zero.p = FALSE, zero.res = FALSE), invPerm(p) is the same as order(p) or sort.list(p) and for that case, the function is equivalent to invPerm. <- function(p) { p[p] <- seq_along(p) ; p }.

Author(s)

Martin Maechler

Examples

  p <- sample(10) # a random permutation vector
  ip <- invPerm(p)
  p[ip] # == 1:10
  ## they are indeed inverse of each other:
  stopifnot(
    identical(p[ip], 1:10),
    identical(ip[p], 1:10),
    identical(invPerm(ip), p)
  )

[Package Matrix version 1.2-12 Index]