duplicates() function

-----Original Message-----
From: r-devel-bounces at r-project.org 
[mailto:r-devel-bounces at r-project.org] On Behalf Of Duncan Murdoch
Sent: Friday, April 08, 2011 8:16 AM
To: Joshua Ulrich
Cc: R-devel at r-project.org
Subject: Re: [Rd] duplicates() function

On 08/04/2011 11:08 AM, Joshua Ulrich wrote:

How about:

y<- rep(NA,length(x))
y[duplicated(x)]<- match(x[duplicated(x)] ,x)

That's a nice solution for vectors.  Unfortunately for me, I have a 
matrix (which duplicated() handles by checking whole rows).  

So a better 
example that I should have posted would be

x <-  cbind(1, c(9,7,9,3,7) )

and I'd still like the same output

 duplicated(x)

[1] FALSE FALSE  TRUE FALSE TRUE

 duplicates(x)

[1] NA NA  1 NA  2


Duncan Murdoch

--
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