Shift all non-duplicates to the start of the array

Given an array filled with 'n' random numbers, each number may or may not be repeated again in the array, (mix of duplicates and unique numbers) shift all non-duplicates to the start of the array. for example, if array is {4,2,17,2,56,2,4} output should be {4,2,17,56...} the remaining part of array can be modified to anything, doesnt matter