Legacy VBA Code Runs Slowly After Adding New Data Processing Feature
Does anyone know how to I'm getting frustrated with Recently started working on a legacy Excel VBA application that processes financial data. The original setup was quite efficient, but after implementing a new feature to aggregate summarized data from several sheets, performance has taken a noticeable hit. Previously, the code executed within a few seconds, but now it sometimes takes several minutes to complete. In the original code, data was pulled from three sheets and summed using simple loops. Here’s a snippet of what that looked like: ```vba Dim ws1 As Worksheet, ws2 As Worksheet, ws3 As Worksheet Set ws1 = ThisWorkbook.Sheets("Sheet1") Set ws2 = ThisWorkbook.Sheets("Sheet2") Set ws3 = ThisWorkbook.Sheets("Sheet3") Dim total As Double Dim i As Long For i = 1 To 1000 total = total + ws1.Cells(i, 1).Value + ws2.Cells(i, 1).Value + ws3.Cells(i, 1).Value Next i ``` This worked fine until the business requirement changed, demanding additional calculations and data from a fourth sheet, along with conditional logic to filter the data based on user inputs. Here’s the more complex logic I implemented: ```vba Dim ws4 As Worksheet Set ws4 = ThisWorkbook.Sheets("Sheet4") Dim totalFiltered As Double Dim j As Long For j = 1 To 1000 If ws4.Cells(j, 2).Value > 100 Then totalFiltered = totalFiltered + ws1.Cells(j, 1).Value + ws2.Cells(j, 1).Value + ws3.Cells(j, 1).Value End If Next j ``` While adding the new feature, I tried optimizing the nested loops by combining calculations into fewer iterations, but the performance still lagged. Community recommendations suggest using arrays for bulk data manipulation instead of working cell by cell. I attempted to implement an array-based approach: ```vba Dim dataArr() As Variant dataArr = ws1.Range("A1:A1000").Value Dim k As Long For k = LBound(dataArr, 1) To UBound(dataArr, 1) ' Perform calculations on dataArr here Next k ``` Despite these changes, the speed hasn't improved significantly. Does anyone have insights or strategies to debug further and enhance the performance of this legacy VBA code? Specific tips on how to efficiently handle data processing in such scenarios would be appreciated. What am I doing wrong? This is part of a larger application I'm building. Any examples would be super helpful.