[R] knn - 10 fold cross validation

[Prof Brian Ripley]

10-fold cross-validation is easily done at R level: there is generic code 
in MASS, the book knn was written to support.

knn and lda have options for leave-one-out cross-validation just because 
there are compuiationally efficient algorithms for those cases.

On Tue, 6 Jun 2006, Liaw, Andy wrote:

> You might want to check out the function tune.knn() in the e1071 package.
>
> Andy
>
>  _____
>
> From: r-help-bounces at stat.math.ethz.ch on behalf of Tim Smith
> Sent: Tue 6/6/2006 8:29 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] knn - 10 fold cross validation [Broadcast]
>
>
>
> Hi,
>
>  I was trying to get the optimal 'k' for the knn. To do this I was using
> the following function :
>
>
> knn.cvk <- function(datmat, cl, k = 2:9) {
>    datmatT <- (datmat)
>  cv.err <- cl.pred <- c()
>
>  for (i in k) {
>    newpre <- as.vector(knn.cv(datmatT, cl, k = i))
>    cl.pred <- cbind(cl.pred, newpre)
>    cv.err <- c(cv.err, sum(cl != newpre))
>
>  }
>  k0 <- k[which.min(cv.err)]
>  print(k0)
>  return(k0)
> }
>
>
>  However, the knn.cv function does a 'leave one out' cross validation. I
> checked the documentation to see if I could change this, but it appears that
> I cannot. Since I have large datasets, I would like to do 10 fold cross
> validation, instead of the 'leave one out'.
>
>
>  Is there some other function that I can use that will give me a 10 fold
> cross validation for KNN ?
>
>  many thanks.
>
> __________________________________________________
>
>
>
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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)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595