[R-sig-eco] keeping a variable as qualitative even if it is coded with numbers
Gi-Mick Wu
mick.wu at mail.mcgill.ca
Mon Nov 29 21:51:44 CET 2010
Hi Amelie,
Could it be ok as it is?
If the only values are 0 & 1, it should similar to coding for a binary qualitative variable (e.g. presence/absence, male/female). I believe qualitative variables are "dummy-coded" with 0-1 anyway in order to calculate almost any statistics on them.
Try this for example:
##### R CODE
# variables
y <- rnorm(100)
xchar <- rep(c("a","b"), 50)
xnum <- rep(c(0,1), 50)
# both linear models give the same result
lm(y~xchar)
lm(y~xnum)
#####
Hope that helps...
Mick
On 2010-11-27, at 3:00 AM, <r-sig-ecology-request at r-project.org> <r-sig-ecology-request at r-project.org> wrote:
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> Today's Topics:
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> 1. keeping a variable as qualitative even if it is coded with
> numbers (amelie_can)
> 2. Re: keeping a variable as qualitative even if it is coded
> with numbers (Chris Howden)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 26 Nov 2010 09:40:38 -0800 (PST)
> From: amelie_can <amelie_qcan at hotmail.com>
> To: r-sig-ecology at r-project.org
> Subject: [R-sig-eco] keeping a variable as qualitative even if it is
> coded with numbers
> Message-ID: <1290793238498-5778025.post at n2.nabble.com>
> Content-Type: text/plain; charset=us-ascii
>
>
> Hello,
>
> I am running a fourthcorner analysis which links species abundance,
> functionnal traits and environmental variable. One of my trait is about seed
> dispersal (qualitative variable) in which I have four classes: wind, water,
> short and long distance. One species can have many types of dispersal. So in
> my original table, I created four different column.
>
> ex:
>
> wind water short long
> sp1 1 1 0 0
> sp2 0 0 1 0
> sp3 0 1 1 1
>
> and so forth. My problem is that those variable are considered as
> quantitative but they are qualitative.
> I tried to transform them using the function as.factor but then it includes
> the 0 in my analysis and I am not interest in that.
>
> Any ideas to make those variable "qualitative"?
>
> Thank you all,
>
> Amelie
> --
> View this message in context: http://r-sig-ecology.471788.n2.nabble.com/keeping-a-variable-as-qualitative-even-if-it-is-coded-with-numbers-tp5778025p5778025.html
> Sent from the r-sig-ecology mailing list archive at Nabble.com.
>
>
>
> ------------------------------
>
> Message: 2
> Date: Sat, 27 Nov 2010 10:17:00 +0930
> From: Chris Howden <chris at trickysolutions.com.au>
> To: amelie_can <amelie_qcan at hotmail.com>, r-sig-ecology at r-project.org
> Subject: Re: [R-sig-eco] keeping a variable as qualitative even if it
> is coded with numbers
> Message-ID: <e833f192445f93f8b8ad310753153925 at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> What do u mean it includes the 0's in your analysis?
>
> Are u sure as.factor is converting them to factors (have a look using
> str(data))
>
> And if as.factor isn't working maybe try creating them as factors using
> factor()
>
> Chris Howden
> Founding Partner
> Tricky Solutions
> Tricky Solutions 4 Tricky Problems
> Evidence Based Strategic Development, IP Commercialisation and Innovation,
> Data Analysis, Modelling, and Training
> (mobile) 0410 689 945
> (fax / office) (+618) 8952 7878
> chris at trickysolutions.com.au
>
> -----Original Message-----
> From: r-sig-ecology-bounces at r-project.org
> [mailto:r-sig-ecology-bounces at r-project.org] On Behalf Of amelie_can
> Sent: Saturday, 27 November 2010 3:11 AM
> To: r-sig-ecology at r-project.org
> Subject: [R-sig-eco] keeping a variable as qualitative even if it is coded
> with numbers
>
>
> Hello,
>
> I am running a fourthcorner analysis which links species abundance,
> functionnal traits and environmental variable. One of my trait is about
> seed
> dispersal (qualitative variable) in which I have four classes: wind,
> water,
> short and long distance. One species can have many types of dispersal. So
> in
> my original table, I created four different column.
>
> ex:
>
> wind water short long
> sp1 1 1 0 0
> sp2 0 0 1 0
> sp3 0 1 1 1
>
> and so forth. My problem is that those variable are considered as
> quantitative but they are qualitative.
> I tried to transform them using the function as.factor but then it
> includes
> the 0 in my analysis and I am not interest in that.
>
> Any ideas to make those variable "qualitative"?
>
> Thank you all,
>
> Amelie
> --
> View this message in context:
> http://r-sig-ecology.471788.n2.nabble.com/keeping-a-variable-as-qualitativ
> e-even-if-it-is-coded-with-numbers-tp5778025p5778025.html
> Sent from the r-sig-ecology mailing list archive at Nabble.com.
>
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