Re: [R] Extracting lists in the dataframe $ format

From: Douglas Bates <bates_at_stat.wisc.edu>
Date: Mon, 04 Jun 2007 16:56:15 -0500

On 6/4/07, Stan Hopkins <stanhopkins_at_comcast.net> wrote:
> I'm new to R and am trying to extract the factors of a dataframe using numeric indices (e.g. df[1]) that are input to a function definition instead of the other types of references (e.g. df$out). df[1] is a list(?) whose class is "dataframe". These indexed lists can be printed successfuly but are not agreeable to the plot() and lm() functions shown below as are their df$out references. Reading the documentation for plot and lm hasn't helped yet. Thanks in advance - Stan.

> > df=data.frame(out=1:4*3,pred1=1:4,pred2=1:4*2)
> > regression=function(tble,a,b)
> + {
> + plot.new()
> + plot(tble[a]~tble[b])
> + lmm=lm(tble[a]~tble[b])
> + abline(lmm)
> + anova(lmm)
> + }
> > df[1]
> out
> 1 3
> 2 6
> 3 9
> 4 12

but df[[1]] is the first column of df in its native form.

I think of the distinction as like the difference between an element of a set, which is what the "[[" function returns, and the subset consisting of a single element, which is what the "[" function returns.



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