Merge data sets by row differening columns [duplicate]

Answer 1

I had to read your question quite a few times before I understood what you were looking for, but maybe you want rbind.fill from plyr:

d1 <- data.frame(x1,x2,x3,x4,x5)
d2 <- data.frame(x1,x3,x4,x5)
d3 <- data.frame(x2,x3,x4,x5)
d4 <- data.frame(x1,x2,x3,x4,x5)

> rbind.fill(d1,d4,d2,d3)
     x1   x2        x3         x4         x5
1     A    a 1.1216923  0.9236393  0.2749292
2     B    b 1.1913278  1.1145664 -0.5070576
3     C    c 0.2837657 -0.6631544 -1.0675885
4     A    a 1.1216923  0.9236393  0.2749292
5     B    b 1.1913278  1.1145664 -0.5070576
6     C    c 0.2837657 -0.6631544 -1.0675885
7     A  1.1216923  0.9236393  0.2749292
8     B  1.1913278  1.1145664 -0.5070576
9     C  0.2837657 -0.6631544 -1.0675885
10     a 1.1216923  0.9236393  0.2749292
11     b 1.1913278  1.1145664 -0.5070576
12     c 0.2837657 -0.6631544 -1.0675885