R help - Nov 2014 - duplicated function

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.

Dennis

Dennis Fisher MD
P < (The "P Less Than" Company)
Phone: 1-866-PLessThan (1-866-753-7784)
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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