Min Date and set analysis

[SI_NY02]

I'm trying create a chart to answer the following question:

How many distinct customers, with date_type = 'Transaction Date', have placed their first order during any calendar year month. 

I've tried:

Count(aggr(If(tran_date = min(tran_date),({<DateType={'Transaction Date'} >}) distinct customer_id)

[SI_NY02]

Update...  corrected formula, does not show an error, but returns all 0.

Count(aggr(If(tran_date = min(tran_date),({<DateType={'Transaction Date'} >}),1), distinct customer_id))

[BrunPierre · Accepted solution]

Try

=Count(distinct {$<DateType={'Transaction Date'}>} Aggr(If(tran_date = Min(total<customer_id> tran_date), customer_id), customer_id))

[SI_NY02]

Thank you BrunPierre!