Counting Old Dates for a Specific Condition

Hi Mentzer ,

Here I suggest you to try this code to create a calculated column.

Count Group in Oldest Date = 
VAR _Oldest_Date =
    CALCULATE (
        MIN ( Table1[Date] ),
        FILTER ( Table1, Table1[ID] = EARLIER ( Table2[ID] ) )
    )
VAR _GROUPinOldestDate =
    CALCULATE (
        SELECTEDVALUE ( Table1[Group] ),
        FILTER (
            Table1,
            Table1[ID] = EARLIER ( Table2[ID] )
                && Table1[Date] = _Oldest_Date
        )
    )
VAR _Count_Group =
    CALCULATE (
        COUNT ( Table1[Group] ),
        FILTER (
            Table1,
            Table1[ID] = EARLIER ( Table2[ID] )
                && Table1[Group] = _GROUPinOldestDate
        )
    )
RETURN
    IF ( Table2[Change Group] > 1, _Count_Group, BLANK () )  

Result is as below.

Best Regards,
Rico Zhou

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