DAX measure or column to calculate first purchase of every user

[ladislaocsulak]

Hello,

I have a table of transactions and I need to make a report in which we only consider the first transaction that each user made.

One way I could solve this is to duplicate the transactions table, sort by ascending date, and remove duplicates from the user field. But I know I could create a DAX measure or DAX column that does it in a more practical way, how could I do it?

Table: transactions of every user

Fields involved: Date (I want the first purchase for every user); User (unique id for every user)

[AUaero · Accepted solution]

Assuming that your model has transactions table, a date table, and a user table:

# First Transaction Date = 
CALCULATE(
    MIN(Transactions[TransactionDate]),
    ALLEXCEPT(
        Transactions,
        Transactions[UserID],
        'Users'
    )
)

See this article on daxpatterns.com for further reading:
New and returning customers – DAX Patterns