[R] Select the last two rows by id group

[Liaw, Andy]

Something like the following should work:

last.n <- function(x, n) {
    last <- nrow(x)
    x[(last - n + 1):last, , drop=FALSE]
}
## Example: get the last two rows.
do.call(rbind, lapply(split(score, score$id), last.n, 2)) 

You might want to add a check in last.n() to make sure that there are at
least n rows to extract.

Andy

From: Lauri Nikkinen
> 
> Hi R-users,
> 
> Following this post 
> http://tolstoy.newcastle.edu.au/R/help/06/06/28965.html , how 
> do I get last two rows (or six or ten) by id group out of the 
> data frame? Here the example gives just the last row.
> 
> Sincere thanks,
> Lauri
> 
> 	[[alternative HTML version deleted]]
> 
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