另一种选择是按行对列Var1和Var2进行排序，然后应用duplicated.

Another option would be to sort columns Var1 and Var2 rowwise and then apply duplicated.

idx <- !duplicated(t(apply(dat[c("Var1", "Var2")], 1, sort)))
dat[idx, ]
#  Var1 Var2 value
#1  ABC  BCD   0.5
#2  DEF  CDE   0.3