How can I check if indices in a single array equal each other?

I'm creating a random array and I want to see if two or more numbers in that array equal each other.

For example, if I get [1 8 6 4 6] I want to know which numbers are equal (which are the two 6's).

I'm doing this because I want to create another array that has the equal numbers and get other random numbers.

So, if I had [1 8 6 4 6] I want to keep the 6's and randomize the other numbers so the next array would be (for example) [5 9 6 1 6] or [6 2 6 3 6], etc.

What's a simple way I can do this without making a bunch of if statements?

Thank you so much!!!

[John D'Errico]

Please don't do this. Deleting your question insults the person who wasted their time answering YOUR question, by preventing that same answer being useful for anyone else in the future.

[Rena Berman]

(Answers Dev) Restored question.

Answer 1

[Joseph Cheng]

you can do this with one if statement and possible no if statements if i spent more time but this should do the trick. by using the outputs of the function unique one can determine what items are unique and then go through and highlight which ones should be kept. Then take the inverse of what you want to keep and use that to define which index positions you want to swap.

x= [1 8 8 6 4 6 2 1 8 8];
[a b c] = unique(x,'stable')
keep = zeros(size(x));
for ind = 1:length(a)
    match = x == x(b(ind));
    if sum(match)>1
       keep = keep+match
    end
end
 toswap = ~keep;
 replace = randi(10,1,sum(toswap));
 x(toswap) = replace