NADA Package: Referencing Data Frame Columns

Specifically, since it has only a single detection indicator column
(ceneq1), it implies that within any single sample either all the 

were detected, or all were not. Not what I would expect.

Don,

   I have been thinking about this and wondered whether the cast format 

appropriate just for the reason there's only a single censored 

I'm glad you confirmed this as the/one problem.

As to your larger question of which layout is appropriate for use with
NADA functions, the answer is that either can be used. The "trick" is 

use the appropriate syntax to extract the values needed to pass the 

to a NADA function.

   And I've not discovered this in the time I spent trying different 

For the long format you subset the rows, then pass the appropriate
columns. Here's one way:

  with(subset(chem, param=='AgDis') , ros(quant,ceneq1))

   This makes a lot of sense. I was thinking that I needed to create 

data frames for each parameter but subsetting on the fly is much more
efficient and elegant.

Hope this helps.

   It certainly does! Thanks.

(p.s., I still think you'll be better off in the long run if you store
site, param, and maybe era, as character objects, not factors.)

   I need to research this because I thought that factors were character
objects used to partition quantities into groups.

a<-sample(letters[1:5], 20, replace=T)
a

a.f<-as.factor(a)
a.f

levels(a.f)

levels(a.f)[2:3]<-"f"
a.f

Regards,

Rich