[R] Accessing the index of factor in by() function

[Ista Zahn]

Hi Merik,
Please keep the mailing list copied.

On Tue, Jul 26, 2011 at 6:44 AM, Merik Nanish <merik.nanish at gmail.com> wrote:
> You can convert my data into a dataframe simply by dat <- data.frame(id,
> month, value). That doesn't help though.

Can you be more specific? What is the problem you are having?

And no, that's not what I'm looking
> for. What I intend to do is for by to loop through the data based on levels
> of "id" factor (1,2, and 3), and for each level, for my function to printout
> the values of "value" and "month" belonging to the section of data with that
> "id".

OK, easy enough:

dat.tmp <- data.frame(id, month, value)
my.plot <- function(dat) {print(dat[, c("id", "value")])}
by(dat.tmp, id, my.plot)

> Right now, I achieve this with a for loop but I want to avoid looping in the
> data as much as possible.

Why? What do you have against loops?

Best,
Ista

>
> On Tue, Jul 26, 2011 at 12:18 AM, Ista Zahn <izahn at psych.rochester.edu>
> wrote:
>>
>> Hi Merik,
>> by() works most easily with data.frames. Is this what you are after?
>>
>> my.plot <- function(dat) { print(dat$value);
>> print(dat$month[dat$id==dat$value]) }
>> by(dat.tmp, id, my.plot)
>>
>> Best,
>> Ista
>>
>> On Mon, Jul 25, 2011 at 9:19 PM, Merik Nanish <merik.nanish at gmail.com>
>> wrote:
>> > 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
>> >
>> >        [[alternative HTML version deleted]]
>> >
>> > ______________________________________________
>> > R-help at r-project.org mailing list
>> > https://stat.ethz.ch/mailman/listinfo/r-help
>> > PLEASE do read the posting guide
>> > http://www.R-project.org/posting-guide.html
>> > and provide commented, minimal, self-contained, reproducible code.
>> >
>>
>>
>>
>> --
>> Ista Zahn
>> Graduate student
>> University of Rochester
>> Department of Clinical and Social Psychology
>> http://yourpsyche.org
>
>



-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org