# Re: [R] Problem with by(... , median)

From: Michal Figurski <figurski_at_mail.med.upenn.edu>
Date: Tue, 10 Jun 2008 10:21:12 -0400

Well,

Yes, that works just fine! Thank you!

```--
Michal J. Figurski
HUP, Pathology & Laboratory Medicine
Xenobiotics Toxicokinetics Research Laboratory
3400 Spruce St. 7 Maloney

Henrique Dallazuanna wrote:

> Try using aggregate:

>
> aggregate(tb[-1], list(tb\$Subject), FUN=median, na.rm = T)
>
> On Tue, Jun 10, 2008 at 10:18 AM, Michal Figurski
> <figurski_at_mail.med.upenn.edu <mailto:figurski_at_mail.med.upenn.edu>> wrote:
>
>     Hello everyone,
>
>     I am new to R, I have been using SAS for a while. Not surprisingly,
>     I find R much better in graphics, which is publication ready right away.
>
>     Recently, I have been trying to calculate some basic statistics
>     using R. I have a dataset of multiple rows per subject. For example:
>
>     Subject Date    Factor1 Factor2 Factor3
>     P1      0.5     1       1       3
>     P1      1       3       2       5
>     P1      2       3       5       NA
>     ...
>     P2      0.5     1       6       4
>     P2      1       2       NA      7
>     P2      2       3       1       2
>     ...
>
>     I wanted to get the 'by subject' statistics of the factors. I used
>     the following code: a=by(dat1, dat1\$Subject, mean, na.rm=TRUE) -
>     this is for a mean.
>     However, when I try that with a 'median', I get an error message. It
>     is strange to me, because with the 'summary' option, I get the
>     median values for all factors separately, among other information.
>     What I need is just a median, because I later need it for plotting.
>     I have read old posts on the archive, and I agree that the action of
>     'median' is according to the documentation. However, I think this is
>     a serious inconvenience, and it should be changed to work in the
>     same way as mean, summary or sd options.
>
>     Nevertheless, accepting the reality, I have a question to all: how
>     to obtain the by-subject medians of factors in such dataset?
>
>
>     --
>     Michal J. Figurski
>     HUP, Pathology & Laboratory Medicine
>     Xenobiotics Toxicokinetics Research Laboratory
>     3400 Spruce St. 7 Maloney
>
>     ______________________________________________
>     R-help_at_r-project.org <mailto:R-help_at_r-project.org> mailing list
>     https://stat.ethz.ch/mailman/listinfo/r-help
>     http://www.R-project.org/posting-guide.html
>     and provide commented, minimal, self-contained, reproducible code.
>
>
>
>
> --
> Henrique Dallazuanna
> Curitiba-Paraná-Brasil
> 25° 25' 40" S 49° 16' 22" O

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