Dear Andrew,
Here is one way:
# Some data
set.seed(1)
mydata<-data.frame(person_id=rep(1:10,10),x=rnorm(100))
mydata
# last register for person_id
with(mydata,tapply(x,person_id,function(x) tail(x,1)))
# test for person_id=1
mydata[mydata$person_id==1,] # see the last number in column 2
HTH,
Jorge
On Fri, Feb 27, 2009 at 2:02 PM, Andrew Ziem <ahz...@gmail.com> wrote:
> I want to find the last record for each person_id in a data frame
> (from a SQL database) ordered by date. Is there a better way than
> this for loop?
>
> for (i in 2:length(history[,1])) {
> if (history[i, "person_id"] == history[i - 1, "person_id"])
> history[i, "order"] = history[i - 1, "order"] + 1 # same person
> else
> history[i, "order"] = 1 # new person
> }
>
> # ignore all records except the last for each con_id
> history2 <- subset(history, order == 1)
>
>
> Andrew
>
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