```
# NOT RUN {
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)
# }
```

Run the code above in your browser using DataLab