Rank with groups and duplicates

Hello guys,

I need some help with a rank column

This is what I have:

I need to rank rpr column inside every rpf value

rpf is a report id and every rpr is a sample inside the report. I need to sort the samples (first, second, third ..... ). the blanks should be sample 0

I need to reach this result:

For every rpf value the rank should restart following the same logic:

rpr = blank -> 0

rank by rpr ascending

Could someone pleasae help me?

Thanks,

Thiago Duarte