[R] id number by group and correlative

[Sarah Goslee]

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.daza at 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.daza at gmail.com
>



-- 
Sarah Goslee
http://www.functionaldiversity.org