DAX equivalent of Excel PERCENTRANK.INC per category - powerbi

Question

I would like to calculate in DAX equivalent of Excel function PERCENTRANK.INC but per Category. I admit that I do not know even how to calculate it for Category. Any hints will be highly appreciated.
Here is M code for sample data:
let
Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WcisqzSwpVtJRSiwoyEkF0oZKsTpIwkmJeUAIZJigipfn56QlpRYVVQLZpqhSyRlQcWOweFhqempJYlJOKlgusagovwTIMMKUK8gvSSzJhzsBRS4/LzM/D0ibo1qFw9HILogFAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Category = _t, Product = _t, Amount = _t]),
#"Changed Type" = Table.TransformColumnTypes(Source,{{"Amount", Int64.Type}})
in
#"Changed Type"

Answer 1

The measure below would produce the desired result. As there is no PERCENTRANK function in DAX, you can manually calculate it from the results of RANKX and COUNTROWS.
Percent Rank Within Category =
IF (
-- This calculation only makes sense if there is only one product
-- in the current filter context. If there are more than one products
-- or no product in the filters, BLANK should be returned.
HASONEVALUE ( MyTable[product] ),
-- Get all products which belong to the same parent category with
-- the product currently being filtered
VAR tbl = CALCULATETABLE (
-- all products, in the modified filter context of...
VALUES ( MyTable[product] ),
-- no filter on product
REMOVEFILTERS ( MyTable[product] ),
-- and under the same parent category
VALUES ( MyTable[Category] )
)
RETURN
CALCULATE (
-- PERCENTRANK = (<rank of product> - 1)
-- / (<total N of products> - 1)
DIVIDE (
-- Sales rank of each product in ascending order
RANKX (
tbl,
CALCULATE ( SUM ( MyTable[Amount] ) ), ,
ASC
) - 1,
-- Total number of products
COUNTROWS ( tbl ) - 1,
-- When there is only one product, it should return 1
1
)
)
)

Answer 2

Here's how I would write it. Very similar to Kosuke's answer but maybe more readable.
Percent Rank =
VAR ProductsInCategory =
CALCULATETABLE ( VALUES ( MyTable[Product] ), ALLSELECTED ( MyTable[Product] ) )
VAR RankProduct =
RANKX ( ProductsInCategory, [Sales],, ASC )
RETURN
IF (
HASONEVALUE ( MyTable[Product] ),
DIVIDE ( RankProduct - 1, COUNTROWS ( ProductsInCategory ) - 1 )
)