Find and count duplicates for Column A in Table 1 using data from Column A in Table 2

Anonymoustrdoan

sorry for late reply. I had been travelling

Please try this Revised MEASURE and see file attached as well

Measure =
VAR mymodel =
    VALUES ( 'Compare Data'[Model] )
VAR mygroup =
    VALUES ( 'Compare Data'[Group] )
RETURN
    CONCATENATEX (
        EXCEPT (
            CALCULATETABLE (
                VALUES ( 'Full Data'[Vendor Name] ),
                FILTER (
                    'Full Data',
                    'Full Data'[Engine Model] IN mymodel
                        && 'Full Data'[Material Group] IN mygroup
                )
            ),
            VALUES ( 'Compare Data'[Name] )
        ),
        [Vendor Name],
        ", "
    )

For Highest Cost Vendor,,use this MEASURE

Highest cost vendor =
VAR mymodel =
    VALUES ( 'Compare Data'[Model] )
VAR mygroup =
    VALUES ( 'Compare Data'[Group] )
RETURN
    CONCATENATEX (
        TOPN (
            1,
            EXCEPT (
                CALCULATETABLE (
                    VALUES ( 'Full Data'[Vendor Name] ),
                    FILTER (
                        'Full Data',
                        'Full Data'[Engine Model] IN mymodel
                            && 'Full Data'[Material Group] IN mygroup
                    )
                ),
                VALUES ( 'Compare Data'[Name] )
            ),
            CALCULATE ( SUM ( 'Full Data'[Repair Cost] ) ), DESC
        ),
        [Vendor Name],
        ", "
    )

For lowest cost vendor

Lowest cost vendor =
VAR mymodel =
    VALUES ( 'Compare Data'[Model] )
VAR mygroup =
    VALUES ( 'Compare Data'[Group] )
RETURN
    CONCATENATEX (
        TOPN (
            1,
            EXCEPT (
                CALCULATETABLE (
                    VALUES ( 'Full Data'[Vendor Name] ),
                    FILTER (
                        'Full Data',
                        'Full Data'[Engine Model] IN mymodel
                            && 'Full Data'[Material Group] IN mygroup
                    )
                ),
                VALUES ( 'Compare Data'[Name] )
            ),
            CALCULATE ( SUM ( 'Full Data'[Repair Cost] ) ), ASC
        ),
        [Vendor Name],
        ", "
    )