duplicates() function
On Fri, Apr 8, 2011 at 11:08 AM, Joshua Ulrich <josh.m.ulrich at gmail.com> wrote:
How about: y <- rep(NA,length(x)) y[duplicated(x)] <- match(x[duplicated(x)] ,x)
I use Joshua's trick all the time. But it might still be nice with a C implementation. While we are discussing duplication, I would also like to see something like duplicated() but which returns TRUE whenever a value is later duplicated, so I can easily select the values of a vector which has are never duplicated. Right now I need to do something like y [ ! y %in% y[duplicated(y)] ] I am only bringing this up because of Duncan's request. Kasper
-- Joshua Ulrich ?| ?FOSS Trading: www.fosstrading.com On Fri, Apr 8, 2011 at 9:59 AM, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
I need a function which is similar to duplicated(), but instead of returning TRUE/FALSE, returns indices of which element was duplicated. ?That is,
x <- c(9,7,9,3,7) duplicated(x)
[1] FALSE FALSE ?TRUE FALSE TRUE
duplicates(x)
[1] NA NA ?1 NA ?2 (so that I know that element 3 is a duplicate of element 1, and element 5 is a duplicate of element 2, whereas the others were not duplicated according to our definition.) Is there a simple way to write this function? ?I have ?an ugly implementation in R that loops over all the values; it would make more sense to redo it in C, if there isn't a simple implementation I missed. Duncan Murdoch
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