asking for a new GP-Pari command

[American Citizen <website.reader3@gmail.com>]

To all:

Recently I had to remove duplicate entries from a vector.

Can GP-Pari create a command which will work with both lists and vectors 
to output duplicate entries?

I am aware that vecsort has flag=8 in vecsort(V,,8) and listsort has 
flag = 1 in listsort(L,1) to remove duplicates, but I need to find them, 
not erase them.

Suppose v = [1,2,3,4,5,3,6]

Then I would like a GP-Pari command called "duplicates(v)" to produce 
the following output.

duplicates(v) = [3]

I tried the naive approach of

% u = Set(v);

%usz = matsize(u)[2];

%vsz = matsize(v)[2];

% if ( usz != vsz,  {do work to find the duplicate entries in the object} );

This would be a great help since my current approach is quite cumbersome.

Randall