Clearing Contents

I have a workbook open with about 22,000 rows in it. It has data like this

A B C D

SD FRED 3 9
SD FRED 4 2
SD FRED 6 27
SF SAM 3 6
SF SAM 4 8
SF SAM 6 1

Now A and B continually shows the same info and C and D are what changes, I
want to clear the contents on columns A and B if it sees the same in A and B
twice, before jumping to the next row. So the data would look like this when
through

A B C D

SD FRED 3 9
4 2
6 27
SF SAM 3 6
4 8
6 1

Same data but it only shows me the vendor and the name once and then
continues on with the rest of the data. Any ideas anyone!!! Thanks in
advance

Sincerely

Sean

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