Date for Last two Friday's Dax

[Anonymous]

Hi 

For this week (today 23th august 2021) - I want to display two dates i.e last two fridays
1) Last Friday i.e 08/20/2021
2) Last Friday before 20th August,2021  i.e 08/13/2021

Can someone please help me with the DAX?

Thank you in advance.

[PaulDBrown · Accepted solution]

OK. First create a Calendar Table. 

Calendar Table =
VAR MinD =
    DATE ( 2020, 12, 01 ) // subsitute for the expression for the minimum date in you model, as in MIN(Table1[Date])
VAR MaxD =
    DATE ( 2021, 10, 31 ) // subsitute for the expression for the maximum date in you model, as in MAX(Table2[Date]) - if the min and max dates are in the same table, use the same table expression.
RETURN
    ADDCOLUMNS (
        CALENDAR ( MinD, MaxD ),
        "WeekDay", WEEKDAY ( [Date], 2 ),
        "WeekNum", WEEKNUM ( [Date] ),
        "Year", YEAR ( [Date] ),
        "YearWeek",
            YEAR ( [Date] ) * 100
                + WEEKNUM ( [Date] )
    )

Add a new calculated column to this table to establish an index for the YearWeek field using:

Index =
RANKX('Calendar Table', 'Calendar Table'[YearWeek],,ASC,Dense)

And you should get this final Calendar Table:

Now create the measure you need:

Last Friday =
VAR YearWeek =
    CALCULATE (
        MAX ( 'Calendar Table'[Index] ),
        FILTER ( 'Calendar Table' , 'Calendar Table'[Date] = TODAY () )
    )
RETURN
    CALCULATE (
        MAX ( 'Calendar Table'[Date] ),
        FILTER (
            'Calendar Table',
            'Calendar Table'[Index] = YearWeek - 1
                && 'Calendar Table'[WeekDay] = 5
        )
    )

And...

2 Friday Ago =
VAR YearWeek =
    CALCULATE (
        MAX ( 'Calendar Table'[Index] ),
        FILTER ( 'Calendar Table' , 'Calendar Table'[Date] = TODAY () )
    )
RETURN
    CALCULATE (
        MAX ( 'Calendar Table'[Date] ),
        FILTER (
            'Calendar Table',
            'Calendar Table'[Index] = YearWeek - 2
                && 'Calendar Table'[WeekDay] = 5
        )
    )

And you will get this:

[PaulDBrown]

do you have a Calendar or Date table? Also, does the week begin on Sunday or Monday?

[Anonymous]

I dont have a calendar nor date table. But I can definately create on based on your suggestion.

[PaulDBrown]

you need one. Also, does the week start on Sunday or Monday?

[Anonymous]

Anything would work. As far as I get to the friday's date

[PaulDBrown · Accepted solution]

OK. First create a Calendar Table. 

Calendar Table =
VAR MinD =
    DATE ( 2020, 12, 01 ) // subsitute for the expression for the minimum date in you model, as in MIN(Table1[Date])
VAR MaxD =
    DATE ( 2021, 10, 31 ) // subsitute for the expression for the maximum date in you model, as in MAX(Table2[Date]) - if the min and max dates are in the same table, use the same table expression.
RETURN
    ADDCOLUMNS (
        CALENDAR ( MinD, MaxD ),
        "WeekDay", WEEKDAY ( [Date], 2 ),
        "WeekNum", WEEKNUM ( [Date] ),
        "Year", YEAR ( [Date] ),
        "YearWeek",
            YEAR ( [Date] ) * 100
                + WEEKNUM ( [Date] )
    )

Add a new calculated column to this table to establish an index for the YearWeek field using:

Index =
RANKX('Calendar Table', 'Calendar Table'[YearWeek],,ASC,Dense)

And you should get this final Calendar Table:

Now create the measure you need:

Last Friday =
VAR YearWeek =
    CALCULATE (
        MAX ( 'Calendar Table'[Index] ),
        FILTER ( 'Calendar Table' , 'Calendar Table'[Date] = TODAY () )
    )
RETURN
    CALCULATE (
        MAX ( 'Calendar Table'[Date] ),
        FILTER (
            'Calendar Table',
            'Calendar Table'[Index] = YearWeek - 1
                && 'Calendar Table'[WeekDay] = 5
        )
    )

And...

2 Friday Ago =
VAR YearWeek =
    CALCULATE (
        MAX ( 'Calendar Table'[Index] ),
        FILTER ( 'Calendar Table' , 'Calendar Table'[Date] = TODAY () )
    )
RETURN
    CALCULATE (
        MAX ( 'Calendar Table'[Date] ),
        FILTER (
            'Calendar Table',
            'Calendar Table'[Index] = YearWeek - 2
                && 'Calendar Table'[WeekDay] = 5
        )
    )

And you will get this:

[Anonymous]

Thank you. This is super-helpful.

[PaulDBrown · Accepted solution]

Happy to have helped.
BTW, if you have date fields in your model you should be using the Calendar table as a dimension table by creating relationships with the corresponding date fields in your model. You can the use Time Intelligence functions in measures, and the fields from the Calendar table in your visuals, filters, slicers, measures etc