On 14/11/12 14:50, 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$person)[i])]
<- seq (1:dim(tmp)[1]) }
my.data$item.number <-
with(my.data,unlist(tapply(1:length(person),person,function(x){1:length(x)})))
cheers,
Rolf Turner
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