R help - May 2010 - (no subject)

Hello
I have a data array with soil variables (caperf), in which the variable
"clay" is factor (as I see entering str(caperf)) . I need to do a
regression model, so I need to have arcilla (=clay) as a numeric variable.? For
that I have entered

as.numeric(as.character(arcilla))

and even entering
 'as.numeric(levels(arcilla))[arcilla]'the variable is resting as
factor, and the linear model is not valid (for my purposes).
The decimal commas have been converted to decimal points, so I have no idea of
what to do.
Thanks a lot


Arantzazu Blanco Bernardeau
Dpto de Qu?mica Agr?cola, Geolog?a y?Edafolog?a? 
Universidad de Murcia-Campus de Espinardo





 		 	   		  
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Dise?ar aplicaciones tiene premio. ?Si eres desarrollador no esperes m?s!

Hi,

Sorry, I'm not really getting what going on here ... perhaps having
more domain knowledge would help me make better sense of our question.

In particular:

On Tue, May 18, 2010 at 11:35 AM, Arantzazu Blanco Bernardeau
<aramucia at hotmail.com> wrote:
>
> Hello
> I have a data array with soil variables (caperf), in which the variable
"clay" is factor (as I see entering str(caperf)) . I need to do a
regression model, so I need to have arcilla (=clay) as a numeric variable.? For
that I have entered
>
> as.numeric(as.character(arcilla))
>
> and even entering
> ?'as.numeric(levels(arcilla))[arcilla]'
The above code doesn't make sense to me ...

Perhaps cleaning up your question and providing some reproducible
example we can use to help show you the light (just describing what a
variable has isn't enough -- give us minimal code we can paste into R
that reproduces your problem).

Alternatively, depending no what your "levels" mean, you might want to
recode your data using "dummy variables" (I'm not sure if
that's the
official term) .. this is what I mean:

http://dss.princeton.edu/online_help/analysis/dummy_variables.htm

In your example, let's say you have four levels for "clay" ...
maybe
"soft", "hard", "smooth", "red"

Instead of only using 1 variable with values 1-4, you would recode
this into 4 variables with values 0,1

So, if one example has a value of "smooth" for clay. Instead of coding
it like:
clay: 3

You would do:
soft: 0
hard: 0
smooth: 1
red : 0

-steve
-- 
Steve Lianoglou
Graduate Student: Computational Systems Biology
 | Memorial Sloan-Kettering Cancer Center
 | Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact