MATLAB: Swap only 2 elements in an array

Question

I'm try to come up with a function that can randomly swap 2 elements (and only 2 at a time) from an array of 20 unique numbers.

Say a=randperm(20) a=[4 1 9 13 5 20 19 ….] would become anew=[19 1 9 13 5 20 4 ….]

Answer 1

This works:

a=[4 1 9 13 5 20 19]
a([1 7]) = a([7 1])
a =
     4     1     9    13     5    20    19
a =
    19     1     9    13     5    20     4