RANKX Function (DAX)
Returns the ranking of a number in a list of numbers for each row in the table argument.
If expression or value evaluates to BLANK it is treated as a 0 (zero) for all expressions that result in a number, or as an empty text for all text expressions.
If value is not among all possible values of expression then RANKX temporarily adds value to the values from expression and re-evaluates RANKX to determine the proper rank of value.
Optional arguments might be skipped by placing an empty comma (,) in the argument list, i.e. RANKX(Inventory, [InventoryCost],,,"Dense")