Excel: sum this row of named ranged columns - excel

Question

I have a dynamic number of columns that i add via VBA. These columns are a named range. How can I sum the current row of all the columns in that named range?
Example:
____| A | B | C | D | E |
1 | | 123 | 100 | aaa | 223 |
2 | | 111 | 101 | eee | 212 |
3 | | 112 | 102 | xxx | 214 |
4 | | 197 | 103 | yyy | 300 |
5 | | 176 | 104 | zzz | 280 |
let's say columns B and C are a named range called ser_ua. I don't know if there will be no columns at all in this named range or if there will be 50 columns. How can i sum the current row "slice" in (in this case) E?

Answer 1

You can 'slice' off a column with the INDEX function, using the MATCH function to find the last number in the first row.
=sum(index(ser_ua, 0, match(1e99, 1:1)))
Any other column could be 'sliced' off using the column_num parameter of INDEX either with a hard-coded number or some formula returning a number.
        
If ser_ua is a named range starting at B2 then you cannot ask for hte column number of the last number in row 1. You would have to ask for the last number on the first row of ser_ua.
=sum(index(ser_ua, 0, match(1E+99, index(ser_ua, 1, 0))))
        

Answer 2

Since you are already using VBA,:
Public Function SumAcross(N As Long) As Variant
Dim wf As WorksheetFunction, RangeToAdd As Range
Set wf = Application.WorksheetFunction
Set RangeToAdd = Intersect(Rows(N), Range("ser_ua"))
SumAcross = wf.Sum(RangeToAdd)
End Function
EDIT#1:
To improve the volatility of the UDF, we can pass it the range being examined:
Public Function SumAcross(r As Range, N As Long) As Variant
Dim wf As WorksheetFunction, RangeToAdd As Range
Set wf = Application.WorksheetFunction
Set RangeToAdd = Intersect(Rows(N), Range("ser_ua"))
SumAcross = wf.Sum(RangeToAdd)
End Function
and in a typical worksheet cell:
=SumAcross(ser_ua,ROW())