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List:       r-help
Subject:    Re: [R] error message in plot(aov-object) -- repost
From:       Peter Dalgaard <p.dalgaard () biostat ! ku ! dk>
Date:       2004-01-16 12:29:36
Message-ID: x2eku0m5zj.fsf () biostat ! ku ! dk
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Uwe Ligges <ligges@statistik.uni-dortmund.de> writes:

> plot.lm() produces the error message, in particular the lines
> 
>     hii <- lm.influence(x, do.coef = FALSE)$hat
> 
> which appears to be 1 in some cases, and
> 
>     rs <- r.w/(s * sqrt(1 - hii))
> 
> (you get a division by zero and the outcome is Inf, hence it's not
> possible to scale the plot any more).
> 
> 
> I'd call it a bug, but I don't know what the bug really is. I'll think
> about it...

If the $hat is 1, then the residual is theoretically zero and you
should get 0/0 == NA which would be much less trouble. 

Apparently, floating poing arithmetic makes it not quite so and you
get Inf in some cases. I'd expect that rs[hii==1] <- NA would fix
things up, although you might possibly need a fuzz factor (hii >
1-1e-10 or so).

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907

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