Here is one way of doing it:

> x <- read.table(textConnection("subject hospital        date_enrollment
hospital_beds
+  1       hospitalA       1/3/2002        300
+  2       hospitalA       1/6/2002        300
+  3       hospitalB       2/4/2002        150
+  4       hospitalC       3/2/2002        200"), header=TRUE)
> closeAllConnections()
> y <- as.Date(x$date_enrollment, "%m/%d/%Y")
> z <- cbind(x, year=format(y, "%Y"), month=format(y, "%m"))
> # partition the data
> z.s <- split(z, list(z$year, z$month, z$hospital), drop=TRUE)
> # now aggregate
> do.call(rbind, lapply(z.s, function(a) data.frame(hospital=a$hospital[1],
cases=nrow(a),
+     year=a$year[1], month=a$month[1], beds=a$hospital[1])))
                   hospital cases year month      beds
2002.01.hospitalA hospitalA     2 2002    01 hospitalA
2002.02.hospitalB hospitalB     1 2002    02 hospitalB
2002.03.hospitalC hospitalC     1 2002    03 hospitalC
>
>
>


On Mon, Jun 9, 2008 at 12:45 PM, Ricardo Pietrobon <pietr007@gmail.com>
wrote:

> I currently have a data set describing human subjects enrolled into an
> international clinical trial, the name of the hospital enrolling this
> human subject, the date when the subject was enrolled, and a vector
> with variables representing characteristics of the site (e.g., number
> of beds in a hospital).  my data sets looks like this:
>
> subject hospital        date_enrollment hospital_beds
> 1       hospitalA       1/3/2002        300
> 2       hospitalA       1/6/2002        300
> 3       hospitalB       2/4/2002        150
> 4       hospitalC       3/2/2002        200
>
> to perform a time series analysis I am now trying to get to a format
> that would give me the following variables:
>
> month   year    site    number_enrolled_subjects        hospital_beds
>
> the data would be displayed on one-month intervals, and number of
> subjects clustered around sites.
>
> any help would be greatly appreciate
>
> thanks
>
>
> Ricardo
>
> ______________________________________________
> R-help@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<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

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