Re: [R-sig-eco] subsetting data in R

[Manuel Spínola]

Thank you very much Gustavo.

That works.

Manuel

On 24/04/2011 08:30 a.m., Gustavo Carvalho wrote:
> pa2<- subset(pa, influencia=="AP")
> pa2$influencia<- factor(pa2$influencia)
> levels(pa2$influencia)
>
> On Sun, Apr 24, 2011 at 11:24 AM, Manuel Spínola<mspinol...@gmail.com>  
> wrote:
>> Thank you very much for your response, Christian, Roman, and Sarah.
>>
>> Sarah,
>>
>> I am trying your suggestion but I cannot see the levels:
>>
>>   >  pa2 = factor(subset(pa, influencia=="AP")$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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>>
>>
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>>
>>


-- 
*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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