PowerPivot Use if statement and a previews value of a row from the same column

[alexobip]

I am trying to find a way of using this formula 

=IF(A2="";"";IF(AND(B2=B1;AF2<>AF1);(AR1+1);IF(AND(B2=B1;AF2=AF1);AR1;IF(B2<>B1;1))))

in power pivot. Is there a way I can do that?

[AlexisOlson]

An exact translation is rather difficult but it's certainly possible to index per group as it appears you're doing here.

See here for how this works:
https://www.myonlinetraininghub.com/numbering-grouped-data-power-query