Using an if then statement in devried comlumn to count rows

Hello I am hoping there is a way to write an if statement for a derived column to count rows?

for example:

Row 35: PRI      7010

Row 100: PRI 7011

I am hoping for a froumlua that when it gets to row 100. it will go back and look at 35 and use that data if the 7010 = 7010, if not use 7011,,,

thanks