How to reduce runtime for code using ranges and string comparisons

Question

I have the following code and it does exactly what I need it to do however, the loop takes far too long to run (3 minutes +). I am new to VBA so I am not exactly sure 1) wha

Answer 1

Accessing a sheet within a loop is very slow. A better approach is to copy the data into a Variant, array loop over the array and then copy the results back to the sheet

Something like this:

Sub Demo()
    Dim i As Long
    Dim datCol3 As Variant
    Dim datCol14 As Variant

    With Sheets("Sheet1")
        ' Copy data into a Variant Array
        datCol3 = .Range(.Cells(1, 3), .Cells(13000, 3)).Formula
        datCol14 = .Range(.Cells(1, 14), .Cells(13000, 14)).Value
        ' Loop over the array
        For i = 2 To 13000
            If datCol3(i, 1) = "Police" And datCol14(i, 1) = "Bi-wkly Uniform Pay" Then
                datCol3(i, 1) = "Police - Uniform"
            End If
        Next
        'Return the results to the sheet
        .Range(.Cells(1, 3), .Cells(13000, 3)).Formula = datCol3
    End With
End Sub