Removing duplicate rows in vi?

Question

I have a text file that contains a long list of entries (one on each line). Some of these are duplicates, and I would like to know if it is possible (and if so, how) to remove

Answer 1

:%s/^\(.*\)\(\n\1\)\+$/\1/gec

or

:%s/^\(.*\)\(\n\1\)\+$/\1/ge

this is my answer for you ,it can remove multiple duplicate lines and only keep one not remove !