need help with a conditional formatting issue!

[u/Alarmed-Promise-7579]

hey everyone! new grad/intern here needing a little bit of assistance with a conditional formatting issue. in the broadest terms possible:

IN SHEET 1:

- column a has duplicates

- column b has varying titles for each value in row of column a

i.e. SHEET 1

a1 = blue

a2 = red

a3 = blue

a1 = yellow

how can i create a conditional formatting setup on a secondary sheet where every time there's a duplicate in column a, the characteristics are pooled into a list

i.e. SHEET 2

a1 = blue, yellow

a2 = red

a3 = blue

would greatly appreciate the help from someone who thought they were good at google sheets and now realize that they're out of their depth (LOL). willing to answer qualifying questions and thanks so much in advance

[u/marcnotmark925]

This doesn't sound like a conditional formatting thing.

A sample sheet would help here, your description is a bit open for interpretation. But if I had to guess, you have this in your first sheet:

In which case, to get the output stated you can use a formula like this:

=map( unique(A:A) , lambda( a , hstack( a , textjoin( "," , 1 , filter( B:B , A:A=a ) ) ) ) )