Hello,

Here are three vectors to give context to my question below:

*id    <- c(1,1,1,1,1,2,2,2,3,3,3))
month <- c(1, 1, 2, 3, 6, 2, 3, 6, 1, 3, 5)
value <- c(10, 12, 11, 14, 16, 12, 10, 8, 14, 11, 15)*

and I want to plot "value" over "month" separately for each "id". Before I
can do that, I need to section both month and value, based on ID. I create a
my.plot function like this (at this point, it doesn't draw any plots, it is
just an effort to help my understand what I'm doing):

*my.plot <- function(y) { print(y); print(month[id==y]) }*

Now, I tried:

*by(value, id, my.plot)*

But of course, it didn't do what I wanted. I realized that the parameter
passed to my.plot, is a "secion of value" per ID, and not the ID value
itself. Question is, how can I get the value of factor ID at each level of
by()?

Please advise,

Merik

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