CONCATENATEX with Multiple Columns

[BekahLoSurdo]

Hi everyone,

Is there a way to take advantage of CONCATENATEX's delimiter feature (specifically: add a comma when there's another item in the list, don't add a comma for the last or only item) across a ROW vs. down a COLUMN?

I need to list blank fields as follows:

Source: 

ID	Field1	Field1Valid	Field2
ABC	123	N
DEF		Y	123
GHI	123	N	123
JKL		N
MNO	123	N
PQR		N	123
STU	123	N	123
VWX		Y

Desired outcome (Field 1 is considered valid for either not being blank OR for Field1Valid = "Y"):

ID	MissingFields
ABC	Field2
DEF
GHI
JKL	Field1, Field2
MNO	Field2
PQR	Field1
STU
VWX	Field2

So far I've tried:

MissingField(s) = 
VAR _F1 = 
    IF( 'Sample'[Field1] <> BLANK() || 'Sample'[Field1Valid] = "Y",
    BLANK(),
    "Field1" )
VAR _F2 =
    IF( 'Sample'[Field2] <> BLANK(),
    BLANK(),
    "Field2" )
RETURN
_F1 & ", " & _F2

MissingField(s) 2 = 
VAR _F1 = 
    IF( 'Sample'[Field1] <> BLANK() || 'Sample'[Field1Valid] = "Y",
    BLANK(),
    "Field1, " )
VAR _F2 =
    IF( 'Sample'[Field2] <> BLANK(),
    BLANK(),
    "Field2" )
RETURN
CONCATENATEX( CALCULATETABLE( 'Sample', ALLEXCEPT( 'Sample', 'Sample'[ID] ) ), _F1 & _F2 )

I am close but I need help with the commas:

Thank you in advance!

[parry2k · Accepted solution]

@BekahLoSurdo add condition in following

MissingField(s) = 
VAR _F1 = 
    IF( 'Sample'[Field1] <> BLANK() || 'Sample'[Field1Valid] = "Y",
    BLANK(),
    "Field1" )
VAR _F2 =
    IF( 'Sample'[Field2] <> BLANK(),
    BLANK(),
    "Field2" )
RETURN
SWITCH( TRUE(),
__F1 == BLANK() && __F2 == BLANK(), "",
__F2 == BLANK(), __F1,
__F1 == BLANK(), __F2,
_F1 & ", " & _F2
)