Counting the rows in a category

Hi Anonymous ,
you can modify the measure like so:

WeeksInQuartile = 
VAR __previousWeek = 'Table'[id_week] - 1
VAR __Result = 
RANKX (
    FILTER( 
        'Table',
        'Table'[id_employee] = EARLIER('Table'[id_employee])
            && 'Table'[quartile] = EARLIER('Table'[quartile])
            && 'Table'[quartile] = CALCULATE(MAX('Table'[quartile]), FILTER(all('Table'), 'Table'[id_week] = __previousWeek))
    ),
    'Table'[id_week],
    'Table'[id_week],
    ASC
)
Return
__Result

Hello Anonymous ,
thanks for taking the time to point out the error in the previous formula.
Please try out this new approach:

WeeksInQuartile =
VAR __StartRangeWeek =
    MAXX (
        FILTER (
            'Table',
            'Table'[id_employee] = EARLIER ( 'Table'[id_employee] )
                && 'Table'[id_week] <= EARLIER ( 'Table'[id_week] )
                && 'Table'[quartile] <> EARLIER ( 'Table'[quartile] )
        ),
        'Table'[id_week]
    )
VAR __EndRangeWeek =
    MINX (
        FILTER (
            'Table',
            'Table'[id_employee] = EARLIER ( 'Table'[id_employee] )
                && 'Table'[id_week] >= EARLIER ( 'Table'[id_week] )
                && 'Table'[quartile] <> EARLIER ( 'Table'[quartile] )
        ),
        'Table'[id_week]
    )
VAR __Result =
    RANKX (
        FILTER (
            'Table',
            'Table'[id_employee] = EARLIER ( 'Table'[id_employee] )
                && 'Table'[quartile] = EARLIER ( 'Table'[quartile] )
                && 'Table'[id_week] > __StartRangeWeek
                && 'Table'[id_week]
                    < IF (
                        __EndRangeWeek = BLANK (),
                        EARLIER ( 'Table'[id_week] ) + 1,
                        __EndRangeWeek
                    )
        ),
        'Table'[id_week],
        'Table'[id_week],
        ASC
    )
RETURN
    __Result

Performance will probably be terrible on large datasets.
A Power Query solution would probably be much faster in this case.