Try tapply().

For example:

tapply(data$Nitrogen,factor(data$Species),mean)

For the Nitrogen column, the mean is calculated for each Species. (if the data 
frame below is in the object data)

Regards,
Annemarie Eigenhuis 

-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On 
Behalf Of Ramsvatn Silje
Sent: donderdag 4 november 2010 13:28
To: R-help@r-project.org
Subject: [R] Sorting data from one column with strings


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.

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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