[R] cv.glm and "longer object length is not a multiple of shorter object length" error

Peter Ehlers ehlers at ucalgary.ca
Fri Jul 22 13:31:48 CEST 2011

On 2011-07-21 17:29, askantik wrote:
> Hi,
> I've done some searching where others have had trouble with this error (or
> "warning" actually), but I'm unable to solve my problem.  I have a data
> sheet with 13 columns and 36 rows.  Each column has exactly the same number
> of rows.  I've created glms and now want to do cross-validation on 2 of
> them.  Please be gentle-- I'm new to R (and statistics, too, for that
> matter).  Any help is greatly appreciated.  Here's my code:
> /library(boot)
> n<-length(total_species)
> cv13.err<- cv.glm(nests,glm13)
> cv13.err.5<- cv.glm(nests,glm13,K=5)
> cv18.err<- cv.glm(nests,glm18)
> cv18.err.5<- cv.glm(nests,glm18,K=5)/
> I get errors starting with the glm18 part.  glm13 is
> *total_species~RH+elev+RH*elev* and glm18 is *total_species~per_cover+RH*
> Does it have something to do with the two glms having different numbers of
> parameters?  I'm not sure why it seems okay with what I've done for glm13,
> but not glm18.  Thanks again for any help.
> *Warning messages:
> 1: In y - yhat :
>    longer object length is not a multiple of shorter object length*

My guess is that per_cover contains at least one missing value.
You could try

  cv.glm(na.omit(nests), glm18)

I tried glm(..., na.action = na.exclude) but cv.glm() appears not (yet)
to be coded to handle padding of missing values.

Peter Ehlers

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