swap only 2 elements in an array

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

[Star Strider]

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

[Erik Lee]

Thanks, but how do I automate this process?

[Star Strider]

This is how I would do it:

a=randperm(20)
idx = randi(20, 1, 2)
a(idx) = a(flip(idx))

This prints out everything so you can verify that it works.

[Erik Lee]

Is there a way I can label the new string 'anew' while keeping the original as 'a'? I need to compare both later.

[Star Strider]

To keep the original vector, returning the switched one as ‘anew’, insert one additional assignment:

a=randperm(20)
anew = a
idx = randi(20, 1, 2)
anew(idx) = anew(flip(idx))

The new line simply duplicates ‘a’ as ‘anew’ and does the same operation on ‘anew’ as it originally did on ‘a’.

[Erik Lee]

Thank you!

[Star Strider]

My pleasure!

Answer 2

[Guillaume]

a = randperm(20)

swapidx = randperm(numel(a), 2);
a(swapidx) = a(fliplr(swapidx))

Answer 3

[Mohammed]

if the array is 2D ( two dimantion ) you can use this and get it how it work

a=[10 20  
  30 40 ]
%For swapping number in Array 2D
%[10 is a 1] & [30 is 2] & [20 is a 3] & 40 is a 4 

a([2 3])=a([3 2])

OUTPUT:
a =
     10     20
     30     40

a =
     10     30
     20     40