To make such a plot, I would have thought your want your data structure to
be:

yourdat:

Column A: Date
Column B; Chemical
Column C: Result
....

After subsetting this to the chemicals you want or doing the subsetting in
your plot command, something like (base R)

boxplot(Result ~ Chemical, subset=yourdat$Chemical %in% c("Ca","Cl",
"Cond","Mg","Na","SO2","TDS"))

You probably can get what you want one way or the other with your current
data structure -- though you may have to use ggplot or trellis -- but it
does appear to be inconvenient.

Whether I'm correct or not in my understanding of your situation, an
important message is: you should choose your data structure to facilitate
the analysis that you have in mind. IMHO, this is one of R's great
strengths: it provides rich facilities for manipulating data tightly
integrated with plotting and analytical capabilities.

Cheers,
Bert

On Wed, Nov 2, 2011 at 9:46 AM, Rich Shepard <rshepard@appl-ecosys.com>wrote:

> On Wed, 2 Nov 2011, Rich Shepard wrote:
>
>   I want a subset of this with only 7 chemicals: Ca, Cl, Cond, Mg, Na, SO4,
>> and TDS.
>>
>
>  I should have also written that what I ultimately want is to create a
> box-and-whisker plot for these 7 chemicals in a single panel. If that can
> be
> done directly from the source data frame without creating another subset, I
> want to learn the syntax for that.
>
> Rich
>
> ______________________________**________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/**listinfo/r-help<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.
>



-- 

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
Website:
http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm

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