Filter by Value code in Measure

[hayali01]

Hello, I want to select certain cost codes in the cost code column to allow divison by another value. In a very simplified version I want to total the cost of the A codes and divide by the average area of A's. I need the formula to write this. 

Cost Code	COST	Area (m2)
A.1	£1	10
A.2	£2	10
A.3	£3	10
A.4	£4	10
B.1	£5	20
B.2	£6	20
B.3	£7	20

[CNENFRNL]

Hi, @hayali01 , why not make a small transformation to the dataset, which saves a lot of trouble and brings about much clarity in authoring measures.

Avg Cost = 
DIVIDE (
    CALCULATE (
        SUM ( 'Table'[COST] ),
        FILTER ( ALL ( 'Table' ), 'Table'[Region] = MAX ( 'Table'[Region] ) )
    ),
    CALCULATE (
        AVERAGE ( 'Table'[Area (m2)] ),
        FILTER ( ALL ( 'Table' ), 'Table'[Region] = MAX ( 'Table'[Region] ) )
    )
)

[amitchandak]

@hayali01 , Create a measure like

calculate(divide(sum(table[COST]), averageX(Table,table[Area (m2)])), filter( Table, left(Table[Cost Code],1) ="A"))

[wdx223_Daniel]

@hayali01 

=VAR _c=LEFT(MAX('Table'[Cost Code]),FIND(".",MAX('Table'[Cost Code]),,99)-1) RETURN  CALCULATE(DIVIDE(SUM('Table'[Cost]),AVERAGE('Table'[Area (m2)]),0),LEFT('Table'[Cost Code],FIND(".",'Table'[Cost Code],,99)-1)=_c)