[R] (no subject)

[Arantzazu Blanco Bernardeau]

Hello
Well, the problem is, that arcilla is the percentage of clay in the soil sample. So, for linear model, I need to work with that number or value. Now, R thinks that arcilla (arcilla means clay in spanish), is a factor, and gives me the value as a factor, so the output of the linear model is
Call:
lm(formula = formula, data = caperf)

Residuals:
       Min         1Q     Median         3Q        Max 
-1.466e+01 -1.376e-15  1.780e-16  2.038e-15  1.279e+01 

Coefficients:
              Estimate Std. Error t value Pr(>|t|)    
(Intercept)    1.68964    6.33889   0.267 0.790221    
arcilla0.9     1.90228    8.90888   0.214 0.831239    
arcilla10      1.26371    7.96734   0.159 0.874212    
arcilla10.3   15.70081    9.05141   1.735 0.085090 .  
arcilla10.4    7.27517    7.72806   0.941 0.348183    
arcilla10.45   7.03879    9.02600   0.780 0.436853    
arcilla10.5    2.41241    8.90827   0.271 0.786954    
arcilla10.65  15.44298    9.03879   1.709 0.089838 .  
arcilla10.7   19.35651    9.04675   2.140 0.034185 *  
arcilla10.9    3.55947    9.18501   0.388 0.698974    

[...]

arcilla9.9     6.31949    7.35724   0.859 0.391892    
arcilla#N/A   24.17959    8.87201   2.725 0.007274 ** 
limo           0.24920    0.04605   5.412 2.76e-07 ***
CO_gkg1        0.21015    0.03931   5.346 3.73e-07 ***
C03Ca          0.01711    0.02727   0.628 0.531337    
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 

Residual standard error: 6.249 on 135 degrees of freedom
  (50 observations deleted due to missingness)
Multiple R-squared: 0.9736,    Adjusted R-squared: 0.9014 
F-statistic: 13.47 on 370 and 135 DF,  p-value: < 2.2e-16 

So, in the desired linear model, arcilla should be just a line, with the valors of the linear model.
I hope you understand better more. If not, I could make an english version of the file to send, so you can try the commands.
Thanks a lot for your help!



Arantzazu Blanco Bernardeau
Dpto de Química Agrícola, Geología y Edafología
Universidad de Murcia-Campus de Espinardo









----------------------------------------
> Date: Tue, 18 May 2010 11:54:20 -0400
> Subject: Re: [R] (no subject)
> From: mailinglist.honeypot at gmail.com
> To: aramucia at hotmail.com
> CC: r-help at r-project.org
>
> 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
>  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
 		 	   		  
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