Modifying code for different columns

[wellsw]

The below formula will remove duplicates based on column A and B it will also apend column D with the values before removing the duplicate.

For the following statement, am I correct in thinking i,1 is referring to column A and i, 2 to Column B . so If I want to have it join with column A and C I just increment the i,2 to i,3??
What is the Chr(2)

 ( txt = Join$(Array(a(i, 1), a(i, 2)), Chr(2))

for this statement would I just change all 3 of the 4's to 5's if I needed to apend column E vice D?

 a(.Item(txt), 4) = a(.Item(txt), 4) & "," & a(i, 4)

Sub Impact_Assesment()
    Sheets("Impact Assesment").Select
    Dim a, i As Long, ii As Long, n As Long, txt As String
    a = Sheets("Consolidated").Range("a1").CurrentRegion
    With CreateObject("Scripting.Dictionary")
        .CompareMode = 1
        For i = 1 To UBound(a, 1)
            txt = Join$(Array(a(i, 1), a(i, 2)), Chr(2))
            If Not .exists(txt) Then
                n = n + 1: .Item(txt) = n
                For ii = 1 To UBound(a, 2)
                    a(n, ii) = a(i, ii)
                Next
            Else

            End If
        Next
    End With
    With Sheets("Impact Assesment").Range("b1").Resize(n, UBound(a, 2))
        .CurrentRegion.ClearContents
        .Value = a
        .Columns.AutoFit
    End With