Alternating coloring groups of rows in Excel

Question

I have an Excel Spreadsheet like this

id | data for id
   | more data for id
id | data for id
id | data for id
   | more data for id
   | even more data for id
id | data for id
   | more data for id
id | data for id
id | data for id
   | more data for id

Now I want to group the data of one id by alternating the background color of the rows

var color = white
for each row
    if the first cell is not empty and color is white
        set color to green
    if the first cell is not empty and color is green
        set color to white
    set background of row to color

Can anyone help me with a macro or some VBA code

Thanks

Answer 1

I use this formula to get the input for a conditional formatting:

=IF(B2=B1,E1,1-E1))    [content of cell E2]

Where column B contains the item that needs to be grouped and E is an auxiliary column. Every time that the upper cell (B1 on this case) is the same as the current one (B2), the upper row content from column E is returned. Otherwise, it will return 1 minus that content (that is, the outupt will be 0 or 1, depending on the value of the upper cell).

Answer 2

I think this does what you are looking for. Flips color when the cell in column A changes value. Runs until there is no value in column B.

Public Sub HighLightRows()
    Dim i As Integer
    i = 1
    Dim c As Integer
    c = 3       'red

    Do While (Cells(i, 2) <> "")
        If (Cells(i, 1) <> "") Then    'check for new ID
            If c = 3 Then
                c = 4   'green
            Else
                c = 3   'red
            End If
        End If

        Rows(Trim(Str(i)) + ":" + Trim(Str(i))).Interior.ColorIndex = c
        i = i + 1
    Loop
End Sub

Answer 3

Based on Jason Z's answer, which from my tests seems to be wrong (at least on Excel 2010), here's a bit of code that happens to work for me :

Public Sub HighLightRows()
    Dim i As Integer
    i = 2 'start at 2, cause there's nothing to compare the first row with
    Dim c As Integer
    c = 2       'Color 1. Check http://dmcritchie.mvps.org/excel/colors.htm for color indexes

    Do While (Cells(i, 1) <> "")
        If (Cells(i, 1) <> Cells(i - 1, 1)) Then 'check for different value in cell A (index=1)
            If c = 2 Then
                c = 34   'color 2
            Else
                c = 2   'color 1
            End If
        End If

        Rows(Trim(Str(i)) + ":" + Trim(Str(i))).Interior.ColorIndex = c
        i = i + 1
    Loop
End Sub