Message-ID: <CA+vqiLE7JqJ_GVMYPTLP7DhrgPDMYHA_VSJo+-sJvW9Kv-k+dQ@mail.gmail.com>
Date: 2013-04-01T18:43:06Z
From: Ista Zahn
Subject: Factor to numeric conversion - as.numeric(as.character(f))[f] - Language definition seems to say to not use this.
In-Reply-To: <CANKYUCJNc14xKv-c97+g-mysX5XtMyS6mH4YtfbgYHHvAMbqCQ@mail.gmail.com>
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.
>
> [[alternative HTML version deleted]]
>
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