Permute the position of a subset of a vector

February 17, 2023

I want to permute a subset of a vector.

For example, say I have a vector (x) and I select a random subset of the vector (e.g., 40% of its values).

What I want to do is output a new vector (x2) that is identical to (x) except the positions of the values within the random subset are randomly swapped.

For example:

x = 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
random subset = 1, 4, 5, 8
x2 could be = 4, 2, 3, 8, 1, 6, 7, 5, 9, 10

Here’s an an example vector (x) and how I’d select the indices of a random subset of 40% of its values. Any help making (x2) would be appreciated!

x <- seq(1,10,1)
which(x%in%sample(x)[seq_len(length(x)*0.40)])

>Solution :

First draw a sample of proportion p from the indices, then sample and re-assign elements with that indices.

f <- \(x, p=0.4) {
  r <- sample(seq_along(x), length(x)*p)
  x[r] <- sample(x[r])
  `attr<-`(x, 'subs', r)  ## add attribute w/ indices that were sampled
}

set.seed(42)
f(x)
#  [1]  8  2  3  4  1  5  7 10  6  9
# attr(,"subs")
# [1]  1  5 10  8

Data: