Convert a Tableau Calculation into Power BI Dax -

Tableau Calculation:

IF First()=0 THEN WINDOW_SUM(COUNTD(ID)) END

1. First(): This function in Tableau returns the index of the current row relative to the first row in the partition. So, First()=0 is used to check if the current row is the first one in the partition.
2. COUNTD(ID): This counts the distinct values of ID.
3. WINDOW_SUM(COUNTD(ID)): This sums the distinct count of ID over the entire window (i.e., partition).
4. IF First()=0 THEN ... END: This ensures that the calculation is performed only for the first row in the window and returns null for other rows.

5. Equivalent DAX Translation:

   Power BI does not have a direct WINDOW_SUM function, but we can achieve similar functionality using a combination of CALCULATE, DISTINCTCOUNT, and FILTER.

    

   Here's a step-by-step approach to translating it into DAX:

   Please try this below:

   DAX

   IF( ISFILTERED([ID]) || RANKX(ALLSELECTED(TableName), TableName[ID], ,ASC) = 1, CALCULATE(DISTINCTCOUNT(TableName[ID])), BLANK() )

    

   Formila Breakup:

   • RANKX: This ranks the rows based on ID. We use RANKX to simulate First()=0 by checking if the rank of the current row is 1.
   • CALCULATE(DISTINCTCOUNT(TableName[ID])): This counts the distinct ID values.
   • BLANK(): If the current row is not the first one (rank is not 1), it returns a blank.

     This DAX formula will return the distinct count of ID only for the first row and will show blank for other rows, similar to how the Tableau calculation works.