duplicated function

x <- c(7, 7, 7, 2, 3, 2)
match(x, x)

ifelse(duplicated(x), match(x, x), 0)

On 18/11/2014 10:23 AM, Dennis Fisher wrote:

R 3.1.1
OS X

Colleagues

When I use the duplicated function, I often need to find both the
duplicates and the original element that was duplicated.  This can be
accomplished with:
        duplicated(OBJECT) | duplicated(OBJECT, fromLast=TRUE)

 From my perspective, an improvement in the duplicated function would be
an option that accomplishes this with a single call to the function.  This
could either be:
        1.  a new option: all=TRUE (pick whatever name makes sense)
        2.  allowing fromLast to take a new value (e.g., NA, in the spirit
of the xpd option in par())

If my suggestion would yield unintended consequences, it can certainly be
ignored.

The duplicated() function is pretty fast, so what's wrong with your original
version?  If you find it to be too much typing, wouldn't it be simplest to
write your own function, e.g.

nonunique <- function(x) duplicated(x) | duplicated(x, fromLast=TRUE)

?

Something I've wanted more than once is a variation on duplicated that
returns the index of the duplicated element, so for example

dupindex(c(7,7,7,2,3,2))

would return

0 1 1 0 0 4

or possibly

1 1 1 4 5 4

Duncan Murdoch