Hello,

I am looking for a method to eliminate rows dupblicates in a backwards
manner, for instance:
I want to keep A B but not B A (see my data.frame test).
Thanks
Hermann

> test
  a u
1 A B
2 A C
3 B A
4 B F
5 C A
6 D W
> dput (test)
structure(list(a = structure(c(1L, 1L, 2L, 2L, 3L, 4L), .Label = c("A",
"B", "C", "D"), class = "factor"), u = structure(c(2L, 3L, 1L,
4L, 1L, 5L), .Label = c("A", "B", "C", "F", "W"), class = "factor")),
.Names = c("a",
"u"), row.names = c(NA, -6L), class = "data.frame")

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