Delete adjacent duplicates

Hi

I am having entries like this in my internal table..

    x             y
    23           12
     -              -
    23           25
     -             12 

.

sort itab by x.

( so it will get changed like this)

 x             y
           -              -
           -             12
           23           25
            23           12 

delete adjacent dupilcates from itab comparing x.

but my requirement is i dont want to delete the blank entries in x.

Thanks and Regards,

Arun Joseph