You could use conditional formatting:
1) Click on cell A1
2) Click format, conditional formatting
3) Change Condition 1 to 'formula is'
4) Enter '=COUNTIF(B:B,A1)>0' into the formula space (without quotes)
5) Click the [Format] button and the 'Patterns' tab
6) Choose a colour
7) Click [OK]
8) Click the format painter
9) Click the 'A' at the top of column A
Everything that is highlighted in the colour of your choice is listed in
column B. Everything not coloured is not in column B:
If you need further help, try
http://www.contextures.com/tiptech.html under
headings 'conditional formatting'
