need help in processing a list

Hi,

I have a list of repetitive elements & non-repetitive elements in it. I need to process this list so that new list has elements only one time

eg : 

A= list ( 1  2  2   3  3  3  4  4  4  4)

the processed list should be like this  B = (1  2  3  4)

Thanks,

Raghu