You don't really need to do all of that, since you can
use group directly. But if you want to have a numeric
value for some reason, here's one possible way:
group <- c("A", "A", "A", "A", "B", "B", "B", "C", "C", "C", "C", "C")
id_group <- as.numeric(as.factor(group))
correlative_group <- unlist(lapply(rle(group)$lengths,
function(x)seq(1, x, by=1)))
cbind.data.frame(group, id_group, correlative_group)
As for your last question:
> PD: Last question. Is there any way to save in a variable the internal that
> R uses (those numbers that appear on left side of a dataframe)?
You mean the row names? See ?row.names
Sarah
2011/2/16 Sebastián Daza <sebastian.d...@gmail.com>:
> Hello everyone,
> I am new in R and I am trying to create a id number (a correlative sequence
> of numbers) by group, and a correlative sequence of numbers inside each
> group (my idea is to get statistics by group without having to aggregate
> the database). Here an example:
>
> group id_group correlative_group
> A 1 1
> A 1 2
> A 1 3
> A 1 4
> B 2 1
> B 2 2
> B 2 3
> C 3 1
> C 3 2
> C 3 3
> C 3 4
> C 3 5
>
> Unfortunately, I have been able to find an explicit lag function to get
> id_group (I know I can get it using aggregate and merge but I'm just
> wondering if there is another way to do it). With regard to the
> correlative_group, I don't have any clue about how to do it.
>
> PD: Last question. Is there any way to save in a variable the internal that
> R uses (those numbers that appear on left side of a dataframe)?
>
> Thank you,
> Sebastian.
> --
> Sebastián Daza
> sebastian.d...@gmail.com
>
--
Sarah Goslee
http://www.functionaldiversity.org
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