PowerBI DAX - Identifying first instance based on multiple criteria

Question

Using DAX to identify first instance of a record

I\'m faced with trying to identify the first instance in a database where someone (identified by the ID column) has pu

Answer 1

This is very similar to an answer I gave to another question (which you can find here).

In that question, the request was to see a running count of rows for the given row's criteria (product, year, etc.). We can modify that slightly to get it to work in your problem.

This is the formula I provided in the answer I linked above. The basic concept is to use the EARLIER functions to get the value from the row and pass it into the filter statement.

Running Count = 
    COUNTROWS(
        FILTER(
            'Data',
            [ProductName] = EARLIER([ProductName]) &&
            [Customer] = EARLIER([Customer]) &&
            [Seller] = EARLIER([Seller]) &&
            [Year] <= EARLIER([Year])
        )
    )

What I would suggest for your problem is to create this as a TRUE/FALSE flag by simply checking if the running count is 1. This formula will evaluate to a Boolean flag.

First Instance = 
    COUNTROWS(
        FILTER(
            'Data',
            [ID] = EARLIER([ID]) &&
            [Product] = EARLIER([Product]) &&
            [Purchase Date] <= EARLIER([Purchase Date])
        )
    ) = 1