[R] Factor to numeric conversion - as.numeric(as.character(f))[f] - Language definition seems to say to not use this.

Ista Zahn istazahn at gmail.com
Mon Apr 1 20:43:06 CEST 2013

Hi Mathew,

In what way are they at odds?

On Mon, Apr 1, 2013 at 1:48 PM, Matthew Lundberg
<matthew.k.lundberg at gmail.com> wrote:
> These two seem to be at odds.  Is this the case?
> >From help(factor) - section Warning:
> To transform a factor f to approximately its original numeric values,
> as.numeric(levels(f))[f] is recommended and slightly more efficient than
> as.numeric(as.character(f)).
> >From the language definition - section 2.3.1:
> Factors are currently implemented using an integer array to specify the
> actual levels and
> a second array of names that are mapped to the integers. Rather
> unfortunately users often
> make use of the implementation in order to make some calculations easier.
> This, however,
> is an implementation issue and is not guaranteed to hold in all
> implementations of R.
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