lda in R vs S

At 09:24 PM 5/6/1999 +0100, Prof Brian D Ripley wrote:

I'm running a discriminant analysis in R (0.64.1) to compare it with SPlus

That's not released until tomorrow!  I guess you have the pre-release,
prerw0641, which is actually of 0.64.0.

Yes.  Actually the pre-release of 0.64.1

4.5R2.  The following command line works fine in SPlus but gives an error
in R.  I've only used R for a little while so I'm not certain here what R
(or lda) is complaining about.  The dependent variable (sarich.na[,3]) is
an alpha categorical variable, if that makes a difference.  I'm using

What's that? The response ought to be a factor, according to the docs:

SAS & SPSS speak.  Alpha categorical variable = factor.

formula: A formula of the form `groups ~ x1 + x2 + ...{}'
         That is, the response is the grouping factor and
         the right hand side specifies the (non-factor)
         discriminators.

version VR5.3 (file name VR5.3pl037.zip).

lda.out<-lda(sarich.na[,3]~., data=sarich.na[,4:32])
Error in model.frame(formula, rownames, variables, varnames, extras,
extranames,  : invalid variable type

Is this an lda issue or an R issue?

It is an R issue. Only logical, integer and real variables are allowed
in R model frames, for as the code says

I haven't delved deeply into R internals yet.  I just started experimenting
with it as I was learning SPlus in parallel.  So at the present time, even
though sarich.na[,3] *is* a factor but with alpha levels, are you saying
that R won't allow this?  

   /* Sanity checks to ensure that the the answer can become */
   /* a data frame.  Be deeply suspicious here! */

Deeply suspicious of what?

But that is not the `right' way to do this in either. Use either

Either?  Are you saying that the formulation above isn't correct in
*either* R or SPlus?  It works fine in SPlus (and sarich.na[,3] is coded as
a factor with levels "AINU", "BUSHMAN", etc...).  But, SPlus also allows
sarich.na[,3] to be on the left side even if it isn't an explicit factor.

Even if it is coded only as a character variable, SPlus allows it, lda
calculates the results, and gives the correct answers.  Presumably if this
isn't the "correct" approach, SPlus or lda is coercing the character
variable to a factor.  This also works in aov and other functions that take
a formula.

data(iris)
names(iris)

lda(species ~ . - Species, data=iris)

lda(Species ~ ., data=iris)
lda(as.matrix(iris[, 1:4]), species)