[R] why sd() can be applied to character vector?

[Prof Brian Ripley]

On 27/10/2012 10:16, Jinsong Zhao wrote:
> Hi there,
>
> In the following example, sd() can be applied to a character vector.
> However, mean() can not be run in a similar way. Why?
>
> I have read sd() man page, however, I don't find information about that
> behavior.

Well, it is there:

        x: a numeric vector or an R object which is coercible to one by
           ‘as.vector’.

 > as.vector(x, 'numeric')
  [1]  1  2  3  4  5  6  7  8  9 10

And it is different from mean() because that is generic and allows many 
other forms of input, whereas for sd() one knows what to coerce to.

>
>  > x <- as.character(1:10)
>  > sd(x)
> [1] 3.02765
>  > mean(x)
> [1] NA
> Warning message:
> In mean.default(x) : argument is not numeric or logical: returning NA
>
> Regards,
> Jinsong
>
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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)
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