What is the Rank index port in Rank transformation?

Rank transformation is an active and Connected transformation. it is used to select bottom or top rank of data this means to select the smallest or largest numeric value in a group or port. rank index port used by Informatica server to store the rank position for each record A Designer can create a rank index port automatically for each rank transformation.For Example, if you create a Rank Transformation that ranks the top 10 products for each quarter, then the rank index numbers products from 1-10.