How to do it...

To implement this recipe, do the following:

1. Create a column in the R04_Table table with the following formula:

Unit Market Share = 'R04_Table'[Unit Sales] / SUMX(ALL('R04_Table'),'R04_Table'[Unit Sales])

2. Create a second column in the R04_Table table with the following formula:

Relative Market Share = 
    VAR __LargestCompetitor = MAX('R04_Table'[Unit Market Share])
    VAR __SecondLargestCompetitor = 
        IF(
            COUNTROWS(
                FILTER(
                    ALL('R04_Table'),
                    'R04_Table'[Unit Market Share] = __LargestCompetitor
                )
            ) > 1,
            __LargestCompetitor,
            MAXX(
                FILTER(
                    ALL('R04_Table'),
                    'R04_Table'[Unit Market Share] <> __LargestCompetitor
                ),
            'R04_Table'[Unit Market Share])
        )
RETURN
    IF(
        [Unit Market Share] = __LargestCompetitor,
        __LargestCompetitor / __SecondLargestCompetitor,
        [Unit Market Share] / __LargestCompetitor
    )

3. Format both the Unit Market Share column and the Relative Market Share column as percentages.