Plotting difference in value between two date ranges

[wdbirch19]

Hi PowerBI community!

I've been going round in circles for a couple of days trying to figure this one out so I decided to reach out for some help.

I'm working with some time series data (example below - my real data is a bit more complex) and want to be able to plot the difference between the first and last value for a given day range. However, I want this value to be on a bar chart that is updated depending on a filter that is on the page. 

For example for the data below if I am sepecting the range Day 1 > Day 4 then the value would be 5.7-1.5=4.2; if I am selecting the range Day 3 > Day 5 then it would be 3.2-1.7=1.5.

Day	Value
1	1.5
2	2.4
3	1.7
4	5.7
5	3.2
6	4.8
7	5.3
8	6.9

I can easily calculate a difference in DAX between each value and the value on Day 0, but this doesn't update with filters etc. 

Any help with this would be hugely appreciated!

[wdbirch19]

Hi @gmsamborn, thank you for your help! That works great 😁 Much appreciated

[gmsamborn · Accepted solution]

Hi @wdbirch19 

Would something like this help?

zMeasure = 
VAR _StartDate = MIN( 'Table1'[Date] )
VAR _EndDate = MAX( 'Table1'[Date] )
VAR _StartVal = 
    CALCULATE(
        MAX( 'Table1'[Value] ),
        'Table1'[Date] = _StartDate
    )
VAR _EndVal = 
    CALCULATE(
        MAX( 'Table1'[Value] ),
        'Table1'[Date] = _EndDate
    )
VAR _Diff = _EndVal - _StartVal
RETURN
    _Diff

OR

zMeasure 2 = 
CALCULATE(
    MAX( 'Table1'[Value] ),
    'Table1'[Date] = MAX( 'Table1'[Date] )
)
-
CALCULATE(
    MAX( 'Table1'[Value] ),
    'Table1'[Date] = MIN( 'Table1'[Date] )
)

I hope this helps.