Clear contents of cell if duplicate

I have data that looks like this:

1     1     1     1
1     1     1     1
1     1     1     1
1     1     1     1
2     1     1     1
2     1     1     1
2     2     2     2

I want 
1     1     1     1
       1     1    1
       1     1    1
       1     1    1
2     1     1    1
       1     1    1
2     2     2    2

I want to check A1 if there are ducplicates delete contents of the cell