Vim deletes duplicate rows

The following command will sort all lines and remove duplicates (Keeping Unique lines ):

:sort u
tips:  here "u" maybe short of the word "unique"  I guess:)

If you need more control, here are some alternatives.

There are two versions, the first leaves only the last line, the second leaves only the first line.

g/^\(.*\)$\n\1$/d
g/\%(^\1$\n\)\@<=\(.*\)$/d

Breakdown of the second version:

g//d <-- Delete the lines matching the regexp
\@<= <-- If the bit following matches, make sure the bit preceding this symbol directly precedes the match
\(.*\)$ <-- Match the line into subst register 1
\%( ) <--- Group without placing in a subst register.
^\1$\n <--- Match subst register 1 followed by end of line and the new line between the 2 lines

In this simple format (matching the whole line), it's not going to 
make much difference, but it will start to matter if you want to do 
stuff like match the first word only.

This does a uniq on the first word in the line, and deletes all but the first line:

G/\ % (^ \ 1 \>. * $ \ n \) \@<=\ (\ K \ + \). * $/d