[R] stepAIC invalid scope argument

[Prof Brian Ripley]

Try not to use the name of an R object ... the error is caused by using 
'df' as the second argument to eval().

It works with DF in place of df.

I don;t understand your subject line: that is not the error message you 
received.

On Mon, 15 Aug 2005, Adaikalavan Ramasamy wrote:

> I am trying to replicate the first example from stepAIC from the MASS
> package with my own dataset but am running into error. If someone can
> point where I have gone wrong, I would appreciate it very much.
>
> Here is an example :
>
> set.seed(1)
> df   <- data.frame( x1=rnorm(1000), x2=rnorm(1000), x3=rnorm(1000) )
> df$y <- 0.5*df$x1 + rnorm(1000, mean=8, sd=0.5)
> # pairs(df); head(df)
>
> lo  <- aov( y ~ 1, data=df )
> hi  <- aov( y ~ .^2, data=df )
> mid <- aov( y ~ x2 + x3, data=df )
>
> Running any of the following commands
>
> stepAIC( mid, scope=list(upper = ~x1 + x2 + x3 , lower = ~1) )
> stepAIC( mid, scope=list(upper = hi , lower = lo) )
> addterm( mid, ~ x1 + x2 + x3 )
> addterm( lo, hi )
>
> gives the same error message :
>  Error in eval(expr, envir, enclos) : invalid second argument
>
> Here is a traceback of the first failed command :
> 14: eval(predvars, data, env)
> 13: model.frame.default(formula = y ~ x2 + x3 + x1, data = df, drop.unused.levels = TRUE)
> 12: model.frame(formula = y ~ x2 + x3 + x1, data = df, drop.unused.levels = TRUE)
> 11: eval(expr, envir, enclos)
> 10: eval(mf, parent.frame())
> 9: lm(formula = y ~ x2 + x3 + x1, data = df, method = "model.frame")
> 8: eval(expr, envir, enclos)
> 7: eval(fcall, env, parent.frame())
> 6: model.frame.lm(fob, xlev = object$xlevels)
> 5: model.frame(fob, xlev = object$xlevels)
> 4: stats:::add1.lm(object, scope = scope, scale = scale)
> 3: addterm.lm(fit, scope$add, scale = scale, trace = max(0, trace - 1), k = k, ...)
> 2: addterm(fit, scope$add, scale = scale, trace = max(0, trace - 1), k = k, ...)
> 1: stepAIC(mid, scope = list(upper = ~x1 + x2 + x3, lower = ~1))
>
> Any pointers would be much appreciated. Thank you.
>
> Regards, Adai
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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