"I'd like to see a cleverer solution that vectorizes..."
and Herve provided it.
Bert Gunter
"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
On Mon, Nov 12, 2018 at 9:43 PM Bert Gunter <bgunter.4...@gmail.com> wrote:
> It is not clear to what you want for the general case. Perhaps:
>
> > v <- letters[c(2,2,1,2,1,1)]
> > wh <- tapply(seq_along(v),factor(v), '[',1)
> > w <- wh[match(v,v[wh])]
> > w
> b b a b a a
> 1 1 3 1 3 3
> > ## and if you want NA's for the first occurences of unique values
> > ## of course:
> > w[wh] <- NA
> > w
> b b a b a a
> NA 1 NA 1 3 3
>
> I'd like to see a cleverer solution that vectorizes and avoids the
> tapply(), though.
>
> Cheers,
> Bert
>
>
>
>
> On Mon, Nov 12, 2018 at 8:33 PM Bert Gunter <bgunter.4...@gmail.com>
> wrote:
>
>> > match(v, unique(v))
>> [1] 1 2 2 1
>>
>> Bert Gunter
>>
>> "The trouble with having an open mind is that people keep coming along
>> and sticking things into it."
>> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>>
>>
>> On Mon, Nov 12, 2018 at 5:08 PM Duncan Murdoch <murdoch.dun...@gmail.com>
>> wrote:
>>
>>> 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
>>>
>>> ______________________________________________
>>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guide
>>> http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
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