Question

I need to sum over a subset of elements in an array of doubles. As a simple example
consider an array of 10 elements:

  Dim Array(1 To 10) As Double 

where each element has been assigned some value. Is there a function in VB that will sum the first 5 elements? Obviously this can be solved using a loop but is there a one line solution? I would like to keep my code consise. I have tried using SUM but without success.

Thanks!

Answer 1

No, there is no built in summing function in VB6 that does what you want, but you can write one easily:

Public Function SumRange(ByRef dblArray() As Double, Optional ByVal StartRange As Long = -1, Optional ByVal Length As Long = -1)

   '-1 on StartRange indicates start at low bound
   If StartRange = -1 Then
      StartRange = LBound(dblArray)
   End If

   '-1 on Length indicates to span all elements to the end of the array
   If Length = -1 Then
      Length = UBound(dblArray) - StartRange - 1
   End If

   Dim dTotal As Double
   Dim lNdx As Long

   For lNdx = StartRange To StartRange + Length - 1
      dTotal = dTotal + dblArray(lNdx)
   Next lNdx

   SumRange = dTotal

End Function

Please be aware I did not sytaz check this, so watch for typos. It can be used as follows:

dResult = SumRange(myArray) 'summ all

dResult = SumRange(myArray, 3) 'sum all starting at offset 3

dResult = SumRange(myArray, , 2) 'sum the the first 2 elements

dResult = SumRange(myArray, 2, 4) 'sum a range start at 2 and with length of 4

You could modify the method to take another optional boolean to specifies if you will tolerate (ignore) out-of-bounds. Right now an error would be reaised if you asked to sum more elements than exist in the array.