On 2010-04-14 21:20, Uwe Dippel wrote:
Referring to "Using R for Data Analysis and Graphics" by J H Maindonald,
and available from the R site, I found the example on p.30 non-working:
> stem(qqnorm(possum$hdlngth))
Error in stem(qqnorm(possum$hdlngth)) : 'x' must be numeric
Since qqnorm(possum$hdlngth) plots, and
> class(possum$hdlngth)
[1] "numeric"
, the problem must be here:
> class(qqnorm(possum$hdlngth))
[1] "list"
Does 'stem' require numerical input? The help says so.
But how to render it numeric?:
> class(as.numeric(qqnorm(possum$hdlngth)))
Error: (list) object cannot be coerced to type 'double'
Can someone please enlighten me about what goes wrong/has changed here?
This is a perfect time to learn about str().
If you check
str(qqnorm(possum$hdlngth))
You will see that it is a list of two numeric vectors. But
stem() expects just one vector. The stem(....) call is an
error; it should be just stem(possum$hdlngth).
-Peter Ehlers
Uwe
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--
Peter Ehlers
University of Calgary
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and provide commented, minimal, self-contained, reproducible code.
