How do I insert while loop inside of function or Group?

hey so i wonder how to put this code inside of a function or group without infinty loop?

when i put the code inside of a function or Group that Loop wont stop and its count up to infinty

scirra.com/tutorials/315/generating-random-numbers-without-duplicates

Why not use a for loop?

Instead of a "while" loop, you can use a for loop from 0 to Array.Width-1.