[R] transforming factor back to numbers

[David Barron]

That's an FAQ:

7.10 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 for the
task at hand (as as.numeric() or unclass() give the internal codes).

On 21/09/06, Rainer M Krug <rkrug at sun.ac.za> wrote:
> Hi
>
> I generate a new dataframe by doing:
>
> npl.agg <- aggregate(npl$DensPlants, list(year=npl$year, sim=npl$sim),
> mean, na.rm=TRUE )
>
> Now I want to plot it by using
>
> coplot(npl.agg$x ~ npl.agg$year | npl.agg$sim, type="l")
>
> but, as npl.agg$year is seen as a factor, the order of the points on the
> x-axis (time axis) does not follow the numerical sorting 1...100, but
> rather the text sorting of the factor npl.agg$year
>
> Is there any way that I can 'defactor' npl.agg$year so that I have again
> the numerical values for year?
>
> Thanks
>
> Rainer
>
> --
> Rainer M. Krug, Dipl. Phys. (Germany), MSc Conservation
> Biology (UCT)
>
> Department of Conservation Ecology and Entomology
> University of Stellenbosch
> Matieland 7602
> South Africa
>
> Tel:            +27 - (0)72 808 2975 (w)
> Fax:            +27 - (0)21 808 3304
> Cell:           +27 - (0)83 9479 042
>
> email:  RKrug at sun.ac.za
>         Rainer at krugs.de
>
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>


-- 
=================================
David Barron
Said Business School
University of Oxford
Park End Street
Oxford OX1 1HP