How to find TopN for each group in Dax

Question

I would like to find the MAX(FYandFW num) based on each Source.

the sample dataset:

Source  FYandFW num sum
Company A   202453  1
Company A   202452  2
Company A   202451  3
Company B   202501  4
Company B   202502  5
Company B   202453  6

What i am trying is below

    Amt = 
VAR i = VALUES('Table'[Source])
VAR j = VALUES('Table'[FYandFW num])
VAR t = 
    TOPN(1,
    CALCULATETABLE('Table', REMOVEFILTERS(), i),
    'Table'[FYandFW num], DESC) 


RETURN
    CALCULATE(SUM('Table'[sum]),t , j)

Expected Answer is Amt = 5 + 1

Answer 1

Try this approach:

Amt = 
  var tSourceMax = 
    SUMMARIZE(
      ALL('Table'),
      'Table'[Source],
      "MaxFYFW", MAX('Table'[FYandFW num])
    )
  RETURN
    SUMX(
      'Table',
      CALCULATE(
        MAX('Table'[sum]),
        FILTER(tSourceMax, 'Table'[Source] = [Source] && 'Table'[FYandFW num] = [MaxFYFW])
      )
    )