# rperm: Draw a Random Permutation Vector with Exchangeability... In sna: Tools for Social Network Analysis

## Description

Draws a random permutation on `1:length(exchange.list)` such that no two elements whose corresponding `exchange.list` values are different are interchanged.

## Usage

 `1` ```rperm(exchange.list) ```

## Arguments

 `exchange.list` A vector such that the permutation vector may exchange the ith and jth positions iff `exchange.list[i]==exchange.list[j]`

## Details

`rperm` draws random permutation vectors given the constraints of exchangeability described above. Thus, `rperm(c(0,0,0,0))` returns a random permutation of four elements in which all exchanges are allowed, while `rperm(c(1,1,"a","a")` (or similar) returns a random permutation of four elements in which only the first/second and third/fourth elements may be exchanged. This turns out to be quite useful for searching permutation spaces with exchangeability constraints (e.g., for structural distance estimation).

## Value

A random permutation vector satisfying the given constraints

## Author(s)

Carter T. Butts [email protected]

`rmperm`
 ```1 2 3 4``` ```rperm(c(0,0,0,0)) #All elements may be exchanged rperm(c(0,0,0,1)) #Fix the fourth element rperm(c(0,0,1,1)) #Allow {1,2} and {3,4} to be swapped rperm(c("a",4,"x",2)) #Fix all elements (the identity permutation) ```