[R] numbering observations: help please!

[Jeff Newmiller]

On Tue, 13 Nov 2012, Paul Artes wrote:

> Dear Friends,
>
> I have the very simple problem of needing to number observations in a data
> frame. After scratching the rest of my hair off my head without inspiration,
> I'm using a silly loop. I'm sure that there is a much more elegant and
> faster solution - can anyone help?
>
> Here is an example:
>
> my.data <- data.frame (person=c(1,1,1,1,2,2,3,3,3,3,3,3,3,4,4,4))   # now I
> want to number those observations sequentially
> # for each person
>
> my.data$item.number <- 0
> for (i in 1:length(unique(my.data$person))) {
> 	my.data$item.number [which (my.data$person == unique(my.data$person)[i])]
> <- seq (1:dim(tmp)[1]) }

Dunno what "tmp" is... but try this:

my.data$item.number <- 1
my.data$item.number <- ave( my.data$item.number, my.data$person, 
FUN=cumsum )

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