DAX for starting number as 0 and subsequent difference in each subgroup

[AdityaG]

Hi all

I would like to convert the following values in the result given below:

Group	Values	Result
A	0	0
A	20	20
A	30	30
B	15	0
B	20	5
B	40	25
C	0	0
C	10	10
C	25	25

Basically, the first value should start from 0, and subsequently, the numbers should be the difference from the value in the first value of the subgroup in the original column.

For instance, for subgroup B, the starting value = 15. Hence the new starting value is 0, 20 is converted to 20-15=5 and 40 to 40-15=25.

Please help me on this. Thanks!

[tamerj1 · Accepted solution]

Hi @AdityaG 

Assuming a calculated column please try

Result =
VAR FirstValue =
CALCULATE ( MIN ( 'Table'[Values] ), ALLEXCEPT ( 'Table', 'Table'[Group] ) )
RETURN
'Table'[Values] - FirstValue