[R] xyplot does not find variable in data

Bert Gunter gunter.berton at gene.com
Mon Oct 12 22:17:25 CEST 2009

>> What principle is at work?
> A strange one called "standard non-standard evaluation"; see
> http://developer.r-project.org/nonstandard-eval.pdf
> for a nice overview by Thomas Lumley.
> ?xyplot says:
>      data: For the 'formula' method, a data frame containing values (or
>            more precisely, anything that is a valid 'envir' argument in
>            'eval', e.g. a list or an environment) for any variables in
>            the formula, as well as 'groups' and 'subset' if applicable.
>            If not found in 'data', or if 'data' is unspecified, the
>            variables are looked for in the environment of the formula.
>            For other methods (where 'x' is not a formula), 'data' is
>            usually ignored, often with a warning.
> so the non-standard evaluation only applies to 'groups' and 'subset'.
> The list may be different for other functions, e.g., densityplot()
> also evaluates 'weights' in 'data'.
> -Deepayan

In addition, you might want to use with, as in:

with( Oats, xyplot(
	yield ~ nitro,scales=list(x=list(at=unique(nitro))), 
) )


-- which standardizes the standard non-standardized evaluation I guess  :-).


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