Excel VBA function weighted average code -- how can I improve this? - excel

Question

I need to write a function that takes a range of values (X) and their associated uncertainties (E) and outputs a weighted average. However, I can't get the function to loop over the array without producing a value error (#VALUE!). I'd also like it to just return the value of X if only one cell is entered as an input for X. Here is where I'm at thus far:
' Calculates the weighted average of arrays of values, X, and their errors, E
Option Explicit
Function WAV(X As Variant, E As Variant) As Double
' Update values upon changing spreadsheet
Application.Volatile
' Test if we have an array or not
If IsArray(X) And IsArray(E) Then
Dim W As Double
Dim WX As Double
W = 0
WX = 0
WAV = 20
For myrow = LBound(X,1) To UBound(X,1)
For mycol = LBound(X, 2) To UBound(X, 2)
'Test if X and E are both numbers and E > 0
If (Application.WorksheetFunction.IsNumber(X(myrow, mycol)) = True) And (Application.WorksheetFunction.IsNumber(E(myrow, mycol)) = True) Then
If E(myrow, mycol) > 0 Then
W = W + 1 / (E(myrow, mycol) ^ 2)
WX = WX + X(myrow, mycol) / (E(myrow, mycol) ^ 2)
End If
End If
Next mycol
Next
If W > 0 Then
WAV = WX / W
End If
Else
WAV = X
End If
End Function
I have wrestled with this for several hours, but to no avail. I'm also a beginner with VBA so I suspect I have made a stupid mistake somewhere. Any help would be appreciated.

Answer 1

Thanks to both BigBen and ScottCraner for their help in answering this question. Here is a working solution incorporating both of their suggestions:
Option Explicit
Function WAV(X As Variant, E As Variant) As Double
' Update values upon changing spreadsheet
Application.Volatile
' Test if we have an array or not
If IsArray(X) And IsArray(E) Then
' Change all the ranges into arrays
Dim XArr() As Variant
Dim EArr() As Variant
Dim WArr() As Variant
' Assign the array values
XArr = X.Value
EArr = E.Value
' Resize the weighting array
ReDim WArr(LBound(EArr, 1) To UBound(EArr, 1), LBound(EArr, 2) To UBound(EArr, 2))
' Calculate square inverses of errors
For myrow = LBound(EArr, 1) To UBound(EArr, 1)
For mycol = LBound(EArr, 2) To UBound(EArr, 2)
WArr(myrow, mycol) = 1 / (EArr(myrow, mycol) ^ 2)
Next mycol
Next myrow
' Now calculate the weighted average using sumproduct function
Dim W As Double
Dim WX As Double
WX = WorksheetFunction.SumProduct(XArr, WArr)
W = WorksheetFunction.SumProduct(WArr)
' Return weighted average
WAV = WX / W
Else
' Return the weighted average
WAV = X
End If
End Function