Tiago,

Assuming the column in x is sorted:

t = which(duplicated(x[, 1]))
x[sort(union(t-1, t)),]

or, if not sorted:

t = which(duplicated(sort(x[, 1])))
x[sort(union(t-1, t)),]

Rob

On Mar 17, 2005, at 6:11 PM, Tiago R Magalhaes wrote:

> Hi
>
> I want to extract all the rows in a data frame that have duplicates
> for a given column.
> I would expect this question to come up pretty often but I have
> researched the archives and surprisingly couldn't find anything.
> The best I can come up with is:
>
> x <- data.frame(a=c(1,2,2,3,3,3), b=10)
> xdup1 <- duplicated(x[,1])
> xdup2 <- duplicated(x[,1][nrow(x):1])[nrow(x):1]
> xAllDups <- x[(xdup1+xdup2)!=0,]
>
> This seems to work, but it's so convoluted that I'm sure there's a
> better method.
> Thanks for any help and enlightenment
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>
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