# [R] Noobie question, regression across levels

Ben Bolker bolker at ufl.edu
Thu Dec 18 14:56:58 CET 2008

```

AllenL wrote:
>
> This is what I ended up using:
>
> Data.subset<-data.frame(PlotFinal,YearFinal,BioFinal,ritFinal)
> ###Subset of main dataset
> Data.length<-sapply(split(Data.subset,PlotFinal),nrow)       ### The
> number of data points in each plot
>
> Data.sub<-split(Data.subset,PlotFinal)         ##Split Data.subset by
> PlotFinal
> Good.levels<-Data.sub[Data.length>10]       ##Take only those Plots that
> have >10 years of observation
>
> lmfun<-function(Good.levels)
> {lm(ritFinal~BioFinal+YearFinal,data=Good.levels)}   ##Set up the
> ###regression function
>

Potentially slightly confusing to have the same name within the lmfun
function ... I probably would
have written this as

lmfun<-function(dat) {lm(ritFinal~BioFinal+YearFinal,data=dat)}

but the results would be identical.

> lmList<-lapply(Good.levels,lmfun)                       ###Apply above
> function to all "good levels"
>
> coef.List<-lapply(lmList,coef)          ###List of the coefficients of
> EACH above regression
>
> This seems to have worked beautifully.
> So, my current problem is extracting the coefficients from "coef.List"
> (and I think this is getting to the roof of my general confusion).
> coef.List seems to be a list of a list of lm objects, right? How come them
> I cannot call them by their position directly (ie. coef.List gives me
> the first lm object. I cannot seem to call the first coefficient in this
> object (the intercept).)
> My goal is to have a bunch of new lists, each one listing a subset of
> coefficients from each regression (ie. one will be a list of all the
> intercepts, another the mean of all the "YearFinal" effects, etc).
>

lmList (not coef.List) should be a list of lm objects, coef.List is a list
of vectors.
I actually think your confusion is simpler/more fundamental.  If you want
the
first element within the first element of coef.List you actually need
coef.List[],
not coef.List ...
You should also consider sapply instead of lapply above, that will give you
a matrix of coefficients (which may be easier to deal with)
--
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