I think Gabor gave you the answer, even if you didn't see it
x <- rep(c("02/27/92", "02/27/92", "01/14/92", "02/28/92", "02/01/92"),each = 5)
z <- data.frame(Date = strptime(x, "%m/%d/%y"))
z$Value <- trunc(runif(25) * 5) + 1
z$State <- c("A","B","C","D","E")[z$Value]
z <- z[order(z$Date),]
z
z[aggregate(1:nrow(z), list(z$State), max)$x,]
Tom
Even if it's not quite right, the technique is there.
> -----Original Message-----
> From: Paul Sorenson [mailto:[EMAIL PROTECTED]
> Sent: Wednesday, 2 February 2005 9:18 AM
> To: [email protected]
> Subject: [R] aggregation with extra columns
>
>
> R People,
>
> Thanks for your help on my recent questions, Excel is never
> going to disappear from my office but with graphics from
> lattice package and some other stuff in R I have been able to
> add some value.
>
> I have a problem I haven't been able to figure out with
> aggregation, I mentioned it earlier but didn't state it very clearly.
>
> Basically I have many "defect events" and I want to grab the
> most recent event for each defect number:
>
> eg:
> "date" "defectnum" "state"
> 2004-12-1 10 create
> 2004-12-2 11 create
> 2004-12-4 10 close
> 2004-12-7 11 fix
>
> to:
> "date" "defectnum" "state"
> 2004-12-4 10 close
> 2004-12-7 11 fix
>
> Now with aggregate I can get the rows I want but not with the
> state "attached":
>
> aggregate(list(date=ev$date), by=list(defectnum=ev$defectnum), max)
>
> Gives me the rows I want but I have lost the "state". I have
> tried doing a merge afterwards but now I realise why they
> warned me avoid using dates as database keys.
>
> What would be handy is somehow getting back the index vector
> from the aggregate function. I realize in the general case
> this wouldn't work for aggregate but in the case of min/max
> the result is a specific record.
>
> Someone earlier mentioned some tricks with sort but I haven't
> been able to make that get to where I want.
>
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