Waterfall value (get value from previous row to populate the next one) with arrayformula

Question

I am traying to resolve this but I think my brain is frozen and I cant find a solution online because I dont know how to correctly describe what I want to be able to find the answer.

So, for example I have this in google sheets,

Level	Category 2
1	Car
2	Hatchback
2	Coupe
2	Convertible
1	Moto
2	Cruiser
2	Scooter

And I want this with the last column automatically expended using arrayformula:

Level	Category 2	Category 1
1	Car	Car
2	Hatchback	Car
2	Coupe	Car
2	Convertible	Car
1	Moto	Moto
2	Cruiser	Moto
2	Scooter	Moto

I want that in column C it will give me the corresponding text to number "1" and then for the rest of the rows it will give me the previous row until it find the next "1"

I was trying with filter, row, ifs but it is not working and my brain is melting, I was able to do that but not using arrayformula, tried to transform to arrayformula but it did not work. I want it to populate automatically. Can I have some help please? (Also I dont like to use query so something that dont use that pls)

Answer 1

You may try:

=scan(,A2:index(A:A,match(,0/(A:A<>""))),lambda(a,c,if(c=1,offset(c,,1),a)))

How Scan() works

---

Alternate using vlookup()

=arrayformula(let(Δ,match(,0/(A:A<>"")), Σ,A2:index(A:A,Δ), Λ,if(row(Σ)*Σ=row(Σ),row(Σ),),
 vlookup(row(Σ),{Λ,B2:index(B:B,Δ)},2,1)))