[R] converting factor to numeric

[kjetil brinchmann halvorsen]

On 21 Aug 2003 at 20:40, kjetil brinchmann halvorsen wrote:

After some private responses I did what I should have done at 
beginning, opened "S Programming" at page 15. It is much clearer than 
the FAQ, which I think is slighly misleading.

Kjetil Halvorsen

> Hola!
> 
> The R FAQ says: 
> 
> 7.12 How do I convert factors to numeric?
> 
> It may happen that when reading numeric data into R (usually, when 
> reading in a file), they come in as factors. If f is such a factor 
> object, you can use
> 
> as.numeric(as.character(f))
> 
> to get the numbers back. More efficient, but harder to remember, is
> 
> as.numeric(levels(f))[as.integer(f)]
> 
> In any case, do not call as.numeric() or their likes directly. 
> 
> But trying to follow the advice:
> 
> (this is without package method attached, but the results are the 
> same with):
> 
> First doing as one shouldn't:
> 
> > table( as.numeric(EdadC) )
> 
>   1   2   3   4   5 
>  20  99 157 127  74 
> 
> Doing as the FAQ says:
> 
> > table( as.numeric(as.character(EdadC)) )
> character(0)
> Warning message: 
> NAs introduced by coercion 
> 
> or:
> 
> > table( as.numeric(levels(EdadC))[as.integer(EdadC)] )
> character(0)
> Warning message: 
> NAs introduced by coercion 
> 
> ?
> 
> Kjetil Halvorsen
> 
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