How to get corresponding price of the smallest date chosen in date slicer in Power BI - charts

Question

I am quite new to working with DAX and Power BI so please don't judge. My problem seems (and might be) simple. Anyways, here we go:
I have a dataset that contains 3 colulmns: Date (date), Price (float), Performance (%)
Attribute descriptions:
Date and Price are constants that are pulled from an external data source. Performance is a variable of the price change over time in percent. It is the percentage change of the price of the current date to the first date in the time-series selection (Selected "from date" of date slicer visual).
I want to create a dynamic line chart that shows performance over time. Difficulty here is when I change the "from date" I want the performance to be variable. Meaning, the price of the chosen "from date" is the new base price and should be calculated accordingly.
Formula:
Date = t, price at date t = pt, performance at date t = pert
Date range:
1.1.2000 to 31.12.2010
Initial situation when "date from" in the date slicer visual = 1.1.2000:
t0 = 1.1.2000
pt0 = 5,00
pert0 = 0%
t5 = 6.1.2000
pt5 = 5,054
pert5 = (pt5-pt0)/pt0 = 1.08%
After changing date slicer so that "from date" is now 10.10.2009:
t0new = 10.10.2009
pt0new = 9,938
pert0new = 0%
t5new = 15.10.2009
pt5new = 9,832
pert5new = (pt5-pt0)/pt0 = -1,05%
As described, I want whatever is selected as starting point from the date slicer as the new base value for the performance calculation and the line chart should adjust accordingly.
I know how to do the dynamic line chart but I cannot figure out the measures and calculated columns I need to do so.
Any help is very much appreciated!
Cheers,
MLU

Answer 1

Calculate the benchmark as the price associated to the first date in
the period. SELECTEDVALUE assumes you have one price per Date,
otherwise use an aggregator (e.g. MIN, MAX, AVERAGE). I use ALLSELECTED so the Benchmark is affected only by Filter Context (slicers) and you can easily use it in visualizations that change the context.
Save our benchmark in a variable for later use
Divide each price by the benchmark. Here we need to apply an aggregator to the Price,
I used AVERAGE assuming you have only one Price per day, therefore, the result is the
price itself.
Here is the measure:
Price vs Dynamic Benchmark :=
VAR vbenchmark = CALCULATE(SELECTEDVALUE(Dataset[Price]),FILTER(ALL( Dataset[Date]), Dataset[Date] = CALCULATE(min(Dataset[Date])), ALLSELECTED(Dataset))
return
AVERAGE(Price) / vbenchmark