User Defined Function - Dynamic Formatting

Hi christsup3r 

In general, a format string expression should return a format string, rather than the result of formatting a value with a format string.

In your case, if you're wanting format strings to be set based on _FormatType and _Scale parameters, you could rewrite your function as follows (I've made some simplifications as well):

DEFINE 
FUNCTION Fn_Formatting = ( _FormatType, _Scale ) =>
VAR CurrencySymbol =
    SWITCH (
        _FormatType,
        "Amounts", "$",
        ""
    )
VAR NumScaleCommas = SWITCH (
        _Scale,
        "B", 3,
        "M", 2,
        "K", 1,
        0
    )
VAR ScaleCommas = REPT ( ",", NumScaleCommas )
VAR FinalFormatString =
    CurrencySymbol & "#,0" & ScaleCommas & ".0" & "\"
        & _Scale
RETURN
    FinalFormatString

Then you could set the dynamic format string of a particular measure to be an expression like any of these:

Fn_Formatting ( "Amount", "K" )

Fn_Formatting ( "Numbers", "M" )

Does this work for you?

See this post for some further demonstrations of UDFs applied to format strings.