[R] Duplicates and duplicated

[Linlin Yan]

On Thu, May 14, 2009 at 2:16 PM, christiaan pauw <cjpauw at gmail.com> wrote:
> Hi everybody.
> I want to identify not only duplicate number but also the original number
> that has been duplicated.
> Example:
> x=c(1,2,3,4,4,5,6,7,8,9)
> y=duplicated(x)
> rbind(x,y)
>
> gives:
>    [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
> x    1    2    3    4    4    5    6    7    8     9
> y    0    0    0    0    1    0    0    0    0     0
>
> i.e. the second 4 [,5] is a duplicate.
>
> What I want is the first and second 4. i.e [,4] and [,5] to be TRUE
>
>    [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
> x    1    2    3    4    4    5    6    7    8     9
> y    0    0    0    1    1    0    0    0    0     0
>

How about

rbind(x, duplicated(x) | duplicated(x, fromLast=TRUE))
  [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
x    1    2    3    4    4    5    6    7    8     9
     0    0    0    1    1    0    0    0    0     0

> I assume it can be done by sorting the vector and then checking is the next
> or the previous entry matches using
> identical() . I am just unsure on how to write such a loop the logic of
> which (I think) is as follows:
>
> sort x
> for every value of x check if the next value is identical and return TRUE
> (or 1) if it is and FALSE (or 0) if it is not
> AND
> check is the previous value is identical and return TRUE (or 1) if it is and
> FALSE (or 0) if it is not
>
> Im i thinking correct and can some help to write such a function
>
> regards
> Christiaan
>
>        [[alternative HTML version deleted]]
>
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