From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>

Date: Thu 11 Jan 2007 - 01:08:36 GMT

> Thank you for your reply. The data argument was exactly the next problem I

*> faced. My workaround involves checking if(missing(data)) then uses different
*

*> calls to oneway.test(). I am certainly interested in other solutions, this
*

*> one is indeed limited.
*

> I do this for the students in the anova class, checking first the homogeneity

*> of variances with fligner.test(), printing the p.value and based on that
*

*> changing the var.equal argument in the oneway.test()
*

*> It's just for convenience, but they do like having it all-in-one.
*

> Best regards,

> Adrian

>

>

Date: Thu 11 Jan 2007 - 01:08:36 GMT

'data' the environment of 'formula' the environment of the caller

and that includes where they look for 'data'. It is easy to use substitute or such to make a literal formula out of 'formula', but doing so changes its environment. So one needs to either

(a) fix up an environment within which to evaluate the modified call that emulates the scoping rules or

(b) create a new 'data' that has references to all the variables needed, and just call the function with the new 'formula' and new 'data'.

At first sight model.frame() looks the way to do (b), but it is not, since if there are function calls in the formula (e.g. log()) the model frame includes the derived variables and not the original ones. There are workarounds (e.g. in glmmPQL), like using all.vars, creating a formula from that, setting its environment to that of the original function and then calling model.frame.

This comes up often enough that I have contemplated adding a solution to (b) to the stats package.

On Tue, 9 Jan 2007, Adrian Dusa wrote:

> On Tuesday 09 January 2007 15:41, Prof Brian Ripley wrote:

>> oneway.test expects a literal formula, not a variable containing a >> formula. The help page says >> >> formula: a formula of the form 'lhs ~ rhs' where 'lhs' gives the >> sample values and 'rhs' the corresponding groups. >> >> Furthermore, if you had >> >> foo.2 <- function() oneway.test(value ~ group) >> >> it would still not work, as >> >> data: an optional matrix or data frame (or similar: see >> 'model.frame') containing the variables in the formula >> 'formula'. By default the variables are taken from >> 'environment(formula)'. >> >> I could show you several complicated workarounds, but why do you want to >> do this? >

> Thank you for your reply. The data argument was exactly the next problem I

>

> I do this for the students in the anova class, checking first the homogeneity

>

> Best regards,

> Adrian

>

>

-- Brian D. Ripley, ripley@stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.Received on Thu Jan 11 12:13:48 2007

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