Rich,
  The documentation for cenboxplot states that the second argument must be 
logical and not integer. the function cenboxplot substitutes synthetic 
values for censored values using ros, hence the error message from the ros 
method.
  I also do not understand how you expect group = 'SO4' to work. It is not 
clear that the function will replicate 'SO4' to make a single group.
Dave

> Date: Tue, 5 Jun 2012 09:58:16 -0700 (PDT)
> From: Rich Shepard <rshepard@appl-ecosys.com>
> To: r-help@r-project.org
> Subject: [R] NADA Applied to my Data
> Message-ID:
>    <alpine.LNX.2.00.1206050931300.27613@salmo.appl-ecosys.com>
> Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII
> 
>    I need a nudge in the right direction to get started using NADA. I 
bought
> Helsel's second addition and am currently reading it; NADA is installed 
in
> R.
> 
>    My data has been restructured with a couple of awk scripts. The data 
frame
> structure now has a flag if the quantity is censored (ceneq1 column) as 
well
> as a lower and upper limit for censored data. For present purposes, 
interval
> censoring can be ignored. The data frame structure is now:
> 
> str(waterchem)
> 'data.frame':   46551 obs. of  7 variables:
>   $ site    : Factor w/ 126 levels "BC-0.5","BC-1",..: 22 22 22 13 3 13 
...
>   $ sampdate: Date, format: "1996-05-22" "1996-07-19" ...
>   $ param   : Factor w/ 58 levels "-0.100","AGP",..: 47 58 10 16 16 26 
...
>   $ quant   : num  0.01 7.69 0.02 63.8 120 0.02 399 439 2 433 ...
>   $ ceneq1  : int  1 0 0 0 0 0 0 0 0 0 ...
>   $ low     : num  0 7.69 0.02 63.8 120 0.02 399 439 2 433 ...
>   $ high    : num  0.01 7.69 0.02 63.8 120 0.02 399 439 2 433 ...
> 
>    What I want to first learn is how to specify a box plot (and whether 
I can
> use the lattice package) for specific chemicals.
> 
> ?cenboxplot shows me the arguments, but I'm not entering them correctly, 
or
> there's a prerequisite step I need to take:
> 
> cenboxplot(waterchem$quant, waterchem$ceneq1, group='SO4', log=T, 
range=1.5)
> Error in function (classes, fdef, mtable)  :
>    unable to find an inherited method for function "ros", for signature
> "numeric", "integer"
> 
>    Perhaps cenboxplot is looking for a separate data set and not a data
> frame? Or, perhaps I need to melt and re-cast the data frame to the wide
> format from the current narrow format? Pointers appreciated.
> 
> Rich
> 
> 
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