RE: [R] extract rows in dataframe with duplicated column values

[Tiago R Magalhaes]

Thank you very much to Andy Liaw, Rob J Goedman and Marc Schwartz for 
taking their time to solve my problem. I've learned in many other 
occasions from useful tips coming from all 3 of them and it just 
happened once again. You got to love this mailing list...

subset(x, a %in% a[duplicated(a)])
works in all cases and it's the simplest, but as always all the 
solutions made me understand a little better the R concepts and 
functions.

I would suggest to include this in the help pages for duplicated.
Also useful might be:
subset(x, !a %in% a[duplicated(a)])
giving all rows that don't have any duplicated
again thanks for all help in this mailing list

Here's one more possibility:
 > subset(x, a %in% a[duplicated(a)])
  a  b
2 2 10
3 2 10
4 3 10
5 3 10
6 3 10
HTH,
Marc Schwartz
On Thu, 2005-03-17 at 22:25 -0500, Liaw, Andy wrote:
 OK, strike one...
 Here's my second try:
 > cnt <- table(x[,1])
 > v <- as.numeric(names(cnt[cnt > 1]))
 > v
 [1] 2 3
 > x[x[,1] %in% v, ]
   a  b
 2 2 10
 3 2 10
 4 3 10
 5 3 10
 6 3 10
 Andy
 > From: Liaw, Andy
 >
 > Does this work for you?
 >
 > > x[table(x[,1]) > 1,]
 >   a  b
 > 2 2 10
 > 3 2 10
 > 5 3 10
 > 6 3 10
 >
 > Andy
 >
 > > From: Tiago R Magalhaes
 > >
 > > 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
 > > >	[[alternative HTML version deleted]]
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