[R] Sorting data from one column with strings

[David Winsemius]

On Nov 4, 2010, at 8:28 AM, Ramsvatn Silje wrote:

>
> Hello,
>
> I have tried to find this out some other way, but unsuccessful I  
> have to
> try this list.
> I assume this should be quite simple.
>
> I have a dataset with 4 columns, "Sample_no", "Species", "Nitrogen",
> "Carbon" in csv format. In the species column I have many different
> species with varying number of obs per species
>
> Eg
>
> "Sample_no"	"Species"	"Nitrogen"	"Carbon"
> 1		Cod		15.2		-19.0
> 2		Haddock	14.8		-20.2
> 3		Cod		15.6		-18.5
> 4		Cod		13.2		-20.1
> 5		Haddock	14.3		-18.8
> Etc..
>
> And I want to calculate, mean, standard dev etc per species for the
> observations "Nitrogen" and "Carbon". And later do plots and stats  
> with
> the different species. I will in the end have many species, so need  
> it to
> be "automatic" I can't enter code for every species separate.
>

http://finzi.psych.upenn.edu/R/library/prettyR/html/brkdn.html

http://finzi.psych.upenn.edu/R/library/Hmisc/html/describe.html
e.g

library(Hmisc)
with( dfrm, describe( ~Species) )

I think you could also probably do lapply(split(dfrm, dfrm$species),  
describe)

the Hmisc::describe function is especially good at first examining a  
vector and applying the appropriate methods to the type of data. There  
are several other packages with different describe functions.

And there are several other packages such as doBy and plyr that will  
offer other concise methods for doing your by-category statistics.

-- 
David.


> Can anyone help me with this? Or if this is the wrong list to sendt  
> this
> question to, where do I send it?
>
> Thank you very much in advance.
>
>
> Best regards
>
> Silje Ramsvatn
>
> PhD-candidate
> University of Tromsø
> Norway
>
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David Winsemius, MD
West Hartford, CT