The duplicated() function gives TRUE if an item in a vector (or row in a
matrix, etc.) is a duplicate of an earlier item. But what I would like
to know is which item does it duplicate?
For example,
v <- c("a", "b", "b", "a")
duplicated(v)
returns
[1] FALSE FALSE TRUE TRUE
What I want is a fast way to calculate
[1] NA NA 2 1
or (equally useful to me)
[1] 1 2 2 1
The result should have the property that if result[i] == j, then v[i] ==
v[j], at least for i != j.
Does this already exist somewhere, or is it easy to write?
Duncan Murdoch
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