[R] Creating dummy variables

From: Arantzazu Blanco Bernardeau <aramucia_at_hotmail.com>
Date: Thu, 03 Jun 2010 14:11:43 +0000

Hello R project
I am a R beginner trying to create a dummy variable to clasificate soil types. So, I have a column in my database called codtipo (typecode in english) where soil type is coded as

1.1 to 1.4 arenosol (I have 4 types)
2.1 to 2.3 calcisols 
4.1 to 4.4 fluvisols

and so on
To make dummy variables I understand that, I create different columns as for gipsisols datos$gipsi=datos$codsuelo
for (i in 1:length(datos$gipsi)){if(datos$codsuelo[i]>=5.1 && (datos$codsuelo[i]<=5.4){datos$gipsi[i]=1}else{0} }
for cambisols it should be
datos$cambi=datos$codsuelo
for (i in 1:length(datos$cambi)){if(datos$codsuelo[i]>=3.1 && datos$codsuelo[i]>=3.3){datos$cambi[i]=1}else{0} }
and so on...
but anyway R answers that a necesary value TRUE/FALSE is not existing. What can I do?
thanks a lot!!

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

> Date: Thu, 3 Jun 2010 06:51:42 -0700
> From: lamprianou_at_yahoo.com
> To: jorismeys@gmail.com
> CC: r-help_at_r-project.org
> Subject: Re: [R] ordinal variables
>
> Thank you Joris,
> I'll have a look into the commands you sent me. They look convincing. I hope my students will also see them in a positive way (although I can force them to pretend that they have a positive attitude)!
>
> Dr. Iasonas Lamprianou
>
>
>
>
>
> Assistant Professor (Educational Research and Evaluation)
>
> Department of Education Sciences
>
> European University-Cyprus
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> P.O. Box 22006
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> --- On Thu, 3/6/10, Joris Meys <jorismeys_at_gmail.com> wrote:
>
> From: Joris Meys <jorismeys_at_gmail.com>
> Subject: Re: [R] ordinal variables
> To: "Iasonas Lamprianou" <lamprianou_at_yahoo.com>
> Cc: r-help_at_r-project.org
> Date: Thursday, 3 June, 2010, 14:35
>
> see ?factor and ?as.factor. On ordered factors you can technically do a spearman without problem, apart from the fact that a spearman test by definition cannot give exact p-values with ties present.
>
> x <- sample(c("a","b","c","d","e"),100,replace=T)
>
> y <- sample(c("a","b","c","d","e"),100,replace=T)
>
> x.ordered <- factor(x,levels=c("e","b","a","d","c"),ordered=T)
>
> x.ordered
> y.ordered <- factor(y,levels=c("e","b","a","d","c"),ordered=T)
> y.ordered
>
> cor.test(x.ordered,y.ordered,method="spearman")
>
> require(pspearman)
>
> spearman.test(x.ordered,y.ordered)
>
> R commander has some menu options to deal with factors. R commander also provides a scripting window. Please do your students a favor, and show them how to use those commands.
>
>
> Cheers
> Joris
>
>
> On Thu, Jun 3, 2010 at 2:25 PM, Iasonas Lamprianou <lamprianou_at_yahoo.com> wrote:
>
> Dear colleagues,
>
>
>
> I teach statistics using SPSS. I want to use R instead. I hit on one problem and I need some quick advice. When I want to work with ordinal variables, in SPSS I can compute the median or create a barchart or compute a spearman correlation with no problems. In R, if I "read" the ordinal variable as numeric, then I cannot do a barplot because I miss the category names. If I read the variables as characters, then I cannot run a spearman. How can I read a variable as numeric, still have the chance to assign value labels, and be able to get table of frequencies etc? I want to be able to do all these things in R commander. My students will probable be scared away if I try anything else other than R commander (just writing commands will not make them happy).
>
>
>
>
> I hope I am not asking for too much. Hopefully there is a way
>
>
>
>
>
>
>
>
>
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> --
> Joris Meys
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