An Excel table has two columns of numbers, and there are duplicates in a column:

Task: First remove duplicates from the columns and then compute their intersection:

Use SPL XLL to do this:

=spl("=[?1,?2].isect(~.group().select(~.len()==1).conj())",A1:A5,B1:B4)

isect()computes the intersection. group() groups data but does not perform aggregation. select() performs filtering operation; ~ is the current member.

Souce:https://www.reddit.com/r/excel/comments/1cndzmh/how_do_i_find_duplicates_across_2_columns_but_not/