[R] squashing some numbers

[Fred J.]

Hello
I have a data frame with many col.s and rows
V4 V5 V6 V7
3  4   5  6
1  4   4  1
2  4   4  1
4  0   5  1

since the data has the middle 2 rows with V5 and V6
are equal, I need to produce
V4 V5 V6 V7
3  4   5  6
            this line removed and the value V7 = 1 is 
     
            added to the next row V7 valuve making it
2
2  4   4  2
4  0   5  1

thanks a lot