[R] unique, but keep LAST occurence
Marc Schwartz (via MN)
mschwartz at mn.rr.com
Mon Jul 24 19:14:23 CEST 2006
On Mon, 2006-07-24 at 12:00 -0500, davidr at rhotrading.com wrote:
> ?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.)
Does this get it?
> DF[sapply(unique(DF$t), function(x) max(which(DF$t == x))), ]
7 1 6
8 2 7
9 3 8
5 4 4
6 5 5
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