Filter expression in Calculate to only pull earliest date

[Anonymous]

This seems like it should be easy but I'm having trouble with syntax. I have a summary table and detail table that are joined together by an ID (1:*).  In my visual, I want to show items from the summary table, with the Earliest PromiseDate from the detail table. No problem - built-in PBI capability. Now, I also want to show the concatenated BuyerID for all the detail rows where the PromiseDate = Earliest PromiseDate. I'm not sure the right syntax to filter this appropriately. Ideas?

Here is the measure I tried on my summary table, but I get the error "A function MIN has been used in a True/False expression that is used as a table filter expression. This is not allowed."

BuyerID Concat = CALCULATE(CONCATENATEX(DISTINCT('Detail'[BuyerID]),'Detail'[BuyerID],", "),MIN('Detail'[PromisedDate]))

The concatenate part works perfectly, except it shows up in the total line.

[Anonymous · Accepted solution]

BuyerID Concat =
CALCULATE(
    CONCATENATEX(
        DISTINCT( 'Detail'[BuyerID] ),
        'Detail'[BuyerID],
        ", "
    ),
    FIRSTDATE( 'Detail'[PromisedDate] )
)

Filters under CALCULATE must always be tables (logical conditions of the form T[Col] = Value are converted into tables under the hood and are what's called syntactic sugar). MIN returns a scalar. FIRSTDATE returns a table.

Depending on your requirements you might need to wrap FIRSTDATE(....) in KEEPFILTERS.