[R] simple loop(?) analysing subsets

[Joshua Wiley]

Hello,

Take a look at ?by

Something like:

by(data, data[ , "species id"], function(x) {lm(o2con ~ bm, data = x)})

As an aside, it can be a bit cumbersome to deal with spaces in a
variables name (because it has to be quoted then).  Also since data is
a function, something like mydata might make it easier to keep code
straight.

HTH,

Josh


On Sun, Jul 18, 2010 at 2:29 PM, karmakiller <roisinmoriarty at gmail.com> wrote:
>
> Hi All,
>
> I have a large data set with many columns of data. One of these columns is a
> species identifier and the remainder are variables such as temperature or
> mass. Currently I am carrying out a single regression on subsets of the data
> set, e.g. separated data sets with only the data from one species at a time.
> I have been searching for a thread that will help me to understand how best
> to repeat this process for each different species identifier in that
> variable column. I can’t seem to find one that is similar to what I am
> trying to do. It might be the case that I am not looking for the right thing
> or that I do not fully understand the process.
>
> How do I run a simple loop that produces a regression for each species as
> identified in the variable species id, which is one column in the large data
> set that I am using?
>
> Simple regression that I wish to repeat
>
> data<- read.table("…/STUDY.txt",header=T)
> names(data)
> model<- with(data,{lm(o2con~bm)})
> summary(model)
>
>
> sample data set
>
> species id      o2con       bm
> 1               0.5         5
> 1               0.6         2
> 1               0.4         4
> 1               0.4         2
> 1               0.5         3
> 2               0.3         7
> 2               0.4         8
> 2               0.5         3
> 2               0.7         4
> 2               0.9         2
> 3               0.3         6
> 3               0.7         2
> 3               0.4         1
> 3               0.3         7
> 5               0.3         2
> 5               0.6         1
> 5               0.9         7
> 5               0.2         5
>
> I would be very grateful for some help with this. I really like using R and
> I can usually figure out what I want to do but I have been trying to figure
> this out for a while now and I am getting nowhere.
>
> Thank you.
>
> --
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>
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>



-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/