什么是Office 365中的Excel中的Power Pivot中的计算列中的正确DAX GROUPBY语法

Question

The following syntax entered into a calculated column formula for table Visits provided below in powerpivot in excel (office 365 version):

=GROUPBY(  
   Visits,  
   [Patient Name],  
   "First_Visit_Date", 
   MINX(CURRENTGROUP(), Visits[Visit_Date])
 )

Yields the error:

The expression refers to multiple columns. Multiple columns cannot be 
converted to a scalar value.

What is the correct DAX GROUPBY syntax when using PowerPivot embedded in Excel to add a calculated column "First_Visit_Date" to the simple source table Visits table depicted below to arrive at the target table also listed below:

Source Table (Visits):

 Patient_Name, Visit_Date, Duration Sue, 8/10/2017, 60 Sue, 8/12/2017, 20 Sue, 8/20/2017, 15 Bill, 9/ 1/2018, 90 Bill, 10/ 1/2018, 90 Sally, 5/22/2016, 30 Sally, 5/30/2016, 30 

Target Table:

 Patient_Name, Visit_Date, Duration, Calculated Column 1 Sue, 8/10/2017, 60, 8/10/2017 Sue, 8/12/2017, 20, 8/10/2017 Sue, 8/20/2017, 15, 8/10/2017 Bill, 9/ 1/2018, 90, 9/ 1/2018 Bill, 10/ 1/2018, 90, 9/ 1/2018 Sally, 5/22/2016, 30, 5/22/2016 Sally, 5/30/2016, 30, 5/22/2016 

Answer 1

Your syntax looks OK, but what you may not realize is that GROUPBY outputs a table, not a scalar value.

This is what your DAX returns if you enter it as a new table rather than a calculated column:

For a calculated column you just want a DAX formula like this:

CalcCol =
CALCULATE(
    MIN(Visits[Visit_Date]),
    ALLEXCEPT(Visits, Visits[Patient_Name])
)

or like this:

CalcCol =
MINX(
    FILTER(
        Visits,
        Visits[Patient_Name] = EARLIER(Visits[Patient_Name])
    ),
    Visits[Visit_Date]
)