Select random cell from a row 4 seperate times

I would like to select a random cell in a row which contains numbers from, say, 1-20. Each number will occur in the row several times. Then repeat the process 4 times with no duplicate numbers, so I have a set of 4 unique numbers, such as 4 - 6 - 12 - 9. Kind of like a lottery, but each number in the hopper may occur several times, but can't be drawn twice. Thank you! Mike