[R] unique, but keep LAST occurence

From: <davidr_at_rhotrading.com>
Date: Tue 25 Jul 2006 - 03:00:02 EST

?unique says


     An object of the same type of 'x'. but if an element is equal to
     one with a smaller index, it is removed.

However, I need to keep the one with the LARGEST index. Can someone please show me the light?
I thought about reversing the row order twice, but I couldn't get it to work right

(My data frame has 125000 rows and 7 columns, and I'm 'uniqueing' on column #1 (chron) only, although the class of the column may not matter.)

Say, e.g.,
> DF <- data.frame(t = c(1,2,3,1,4,5,1,2,3), x = c(0,1,2,3,4,5,6,7,8))

I would like the result to be (sorted as well)  t x
 1 6
 2 7
 3 8
 4 4
 5 5

If I got the original rownames, that would be a bonus (for debugging.)

> R.version

platform       i386-pc-mingw32           
arch           i386                      
os             mingw32                   
system         i386, mingw32             
major          2                         
minor          3.1                       
year           2006                      
month          06                        
day            01                        
svn rev        38247                     
language       R                         
version.string Version 2.3.1 (2006-06-01)

Thanks for any hints!

David L. Reiner
Rho Trading Securities, LLC
Chicago  IL  60605

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