Thank you very much for your response, Christian, Roman, and Sarah.
Sarah,
I am trying your suggestion but I cannot see the levels:
> pa2 = factor(subset(pa, influencia=="AP")$influencia)
> levels(pa2$influencia)
Error in pa2$influencia : $ operator is invalid for atomic vectors
Best,
Manuel
On 24/04/2011 07:51 a.m., Sarah Goslee wrote:
> By default, read.csv() turns character variables into factors, using all the
> unique values as the levels.
>
> subset() retains those levels by default, as they are a vital element of the
> data. If you are studying some attribute of men and women, say height,
> even if you are only looking at the heights for women it's important to
> remember
> that men still exist.
>
> If you don't want influencia to be a factor, you can change that in the import
> stringsAsFactors=FALSE.
>
> If you do want influencia to be a factor, but want the unused levels to be
> removed, you can use factor() to do that.
>
>> testdata<- data.frame(group=c("A", "B", "C", "A", "B", "C"), value=1:6)
>> testdata
> group value
> 1 A 1
> 2 B 2
> 3 C 3
> 4 A 4
> 5 B 5
> 6 C 6
>> str(testdata)
> 'data.frame': 6 obs. of 2 variables:
> $ group: Factor w/ 3 levels "A","B","C": 1 2 3 1 2 3
> $ value: int 1 2 3 4 5 6
>> subset(testdata, group=="A")
> group value
> 1 A 1
> 4 A 4
>> subset(testdata, group=="A")$group
> [1] A A
> Levels: A B C
>> ?subset
>> factor(subset(testdata, group=="A")$group)
> [1] A A
> Levels: A
>
> Sarah
>
> On Sun, Apr 24, 2011 at 9:04 AM, Manuel Spínola<mspinol...@gmail.com> wrote:
>> Dear list members,
>>
>> I have a question regarding too subsetting a data set in R.
>>
>> I created an object for my data:
>>
>> >pa = read.csv("espec_indic.csv", header = T, sep=",", check.names = F)
>>
>> > levels(pa$influencia)
>> [1] "AID" "AII" "AP"
>>
>> The object has 3 levels for influencia (AP, AID, AII)
>>
>> Now I subset only observations with influencia = "AID"
>>
>> >pa2 = subset(pa, influencia=="AID")
>>
>> but if I ask for the levels of influencia still show me the 3 levels,
>> AP, AID, AII.
>>
>> > levels(pa2$influencia)
>> [1] "AID" "AII" "AP"
>>
>> Why is that?
>>
>> I was thinking that I was creating a new data frame with only AID as a
>> level for influencia.
>>
>> How can I make a complete new object with only the observations for
>> "AID" and that the only level for influencia is indeed "AID"?
>>
>> Best,
>>
>> Manuel
>>
>>
--
*Manuel Spínola, Ph.D.*
Instituto Internacional en Conservación y Manejo de Vida Silvestre
Universidad Nacional
Apartado 1350-3000
Heredia
COSTA RICA
mspin...@una.ac.cr
mspinol...@gmail.com
Teléfono: (506) 2277-3598
Fax: (506) 2237-7036
Personal website: Lobito de río
<https://sites.google.com/site/lobitoderio/>
Institutional website: ICOMVIS <http://www.icomvis.una.ac.cr/>
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