How to merge strings and skip duplicates?

Question

Let's say you have a product information sheet that includes columns like "Material", "Finish", and "Color":

Glass   Aqua            Blue
Glass   Clear           Clear
Glass   Clear           Brass
Brass   Polished Brass  Brass

And you want to concatenate them, but without duplicating, so the end result will be:

Glass, Aqua, Blue
Glass, Clear
Glass, Clear, Brass
Brass

(So it skips the 2nd Clear in Line 2, and the 2 cells containing "Brass" in Line 4.)

Any solutions, or even suggestions as to which functions to play with, would be appreciated.

Answer 1

try:

=ARRAYFORMULA(IFNA(REGEXEXTRACT(
 IFNA(REGEXEXTRACT(B:B, A:A), A:A&", "&B:B), C:C), 
 IFNA(REGEXEXTRACT(B:B, A:A), A:A&", "&B:B)&", "&C:C))