R help - Dec 2006 - lattice: defining an own function using args for "formula" and "groups"

x.fun <- function( formula, data ) dotplot( formula, data )
x.grp <- function( formula, groups, data ) dotplot( formula, groups, data )

data( barley )
> x.fun( variety ~ yield | site, data=barley )
# no problem
> dotplot( variety ~ yield | site, groups=year, data=barley )
# no problem
> x.grp( variety ~ yield | site, groups=year, data=barley )
object "year" not found 	# that's my error, so I do:
> x.grp( variety ~ yield | site, groups=barley$year, data=barley )
Error in eval(expr, envir, enclos) : numeric 'envir' arg not of length
one
> traceback()
9: eval(substitute(groups), data, environment(formula))
8: bwplot.formula(x = formula, data = c(2, 2, 2, 2, 2, 2, 2, 2,  ...

Why it is a problem calling x.grp() and no problem calling x.fun() ?
What could I do to get work x.grp() ?

Thanks - Wolfram

Don't know of a more straight forward way but this works. It constructs
a new call to bwplot from the one to x.grp2 and evaluates it in the
parent environment:

library(lattice)
x.grp2 <- function(x, groups, data) {
    cl <- match.call()
    cl[[1]] <- as.name("bwplot")
    eval.parent(cl)
}

x.grp2( variety ~ yield | site, year, barley )


On 12/8/06, Wolfram Fischer <wolfram at fischer-zim.ch>
wrote:
>
> x.fun <- function( formula, data ) dotplot( formula, data )
> x.grp <- function( formula, groups, data ) dotplot( formula, groups,
data )
>
> data( barley )
>
> > x.fun( variety ~ yield | site, data=barley )
> # no problem
>
> > dotplot( variety ~ yield | site, groups=year, data=barley )
> # no problem
>
> > x.grp( variety ~ yield | site, groups=year, data=barley )
> object "year" not found         # that's my error, so I do:
>
> > x.grp( variety ~ yield | site, groups=barley$year, data=barley )
> Error in eval(expr, envir, enclos) : numeric 'envir' arg not of
length one
>
> > traceback()
> 9: eval(substitute(groups), data, environment(formula))
> 8: bwplot.formula(x = formula, data = c(2, 2, 2, 2, 2, 2, 2, 2,  ...
>
> Why it is a problem calling x.grp() and no problem calling x.fun() ?
> What could I do to get work x.grp() ?
>
> Thanks - Wolfram
>
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