R devel - Jan 2010 - Residual DF of NLS models (PR#14194)

Full_Name: Henrik Aalborg Nielsen
Version: 2.10
OS: Linux (SLES 10 / openSUSE 11.1)
Submission from: (NULL) (77.66.63.89)


There seems to be a bug in df.residual.nls which is triggered when nls is called
with argument na.action = na.exclude; in that case 'resid(object)' will
contain
NA-values which should be disregarded when counting the number of residuals:

df.residual.nls <- function(object, ...) {
    w <- object$weights
    n <- if(!is.null(w)) sum(w != 0) else length(resid(object))
    n - length(coef(object))
}

The bug cause the F-test of anova.nls to be wrong.

Replace 'length(resid(object))' with
'sum(!is.na(resid(object)))' ?

... and thank you for producing this fantastic software!

BR
Henrik

Can we please have a reproducible example (as we did ask in the 
FAQ, the posting guide ...).

On Tue, 26 Jan 2010, han at enfor.dk wrote:
> Full_Name: Henrik Aalborg Nielsen
> Version: 2.10
> OS: Linux (SLES 10 / openSUSE 11.1)
> Submission from: (NULL) (77.66.63.89)
>
>
> There seems to be a bug in df.residual.nls which is triggered when nls is
called
> with argument na.action = na.exclude; in that case 'resid(object)'
will contain
> NA-values which should be disregarded when counting the number of
residuals:
>
> df.residual.nls <- function(object, ...) {
>    w <- object$weights
>    n <- if(!is.null(w)) sum(w != 0) else length(resid(object))
>    n - length(coef(object))
> }
>
> The bug cause the F-test of anova.nls to be wrong.
>
> Replace 'length(resid(object))' with
'sum(!is.na(resid(object)))' ?
>
> ... and thank you for producing this fantastic software!
>
> BR
> Henrik
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
-- 
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)
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