[R] lda from MASS function
ripley at stats.ox.ac.uk
Wed Jul 3 21:04:28 CEST 2002
On Wed, 3 Jul 2002, Rishabh Gupta wrote:
> Hi all,
> I am using the lda function from the MASS library to measure the discriminance of different variables with respect to different
> grouping variables by using
> lda( RESULTVARS[, 1:750] , GROUPVAR , tol=0 ) where RESULTVARS contains some 750 different variables.
> Occasionally there is a variable within RESULTVARS that has the same values for all values of GROUPVAR, ie no variance so I get the
> Error in svd(X, nu = 0) : NA/NaN/Inf in foreign function call (arg 1)
> As I understand it, this is due to the a division of zero in one svd function that is used by lda. The nature of my results are such
> that every now and than I will get a case where all the values for a RESULTVARS variable are constant. Is there a way of getting
> past this problem. For example, by using the tol=0 parameter I can avoid problems when the variables are the same within a
> particular group. As far as I am concerned, cases where the variables are constant across all groups is saying that that variable
> has zero discriminance.
You are wrong: that is what the tol argument is for.
You need to delete the constant variables, which contradict the lda model.
Do you really believe is multivariate normality for 750 dimensions?
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)
1 South Parks Road, +44 1865 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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