[R] Extracting lists in the dataframe $ format

[Sarah Goslee]

This is a subset problem, not a problem with plot or lm. You need to
read eg  help("[.data.frame")


Here are two working examples:

# df already means something!
mydf <- 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)
}

regression(mydf, 1, 3)

regression <- function(tble,a,b)
{
           plot.new()
           plot(tble[[a]]~tble[[b]])
           lmm=lm(tble[[a]]~tble[[b]])
           abline(lmm)
           anova(lmm)
}

regression(mydf, 1, 3)

Sarah

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
> > df
>   out pred1 pred2
> 1   3     1     2
> 2   6     2     4
> 3   9     3     6
> 4  12     4     8
> > regression(df,1,3)
> Error in model.frame(formula, rownames, variables, varnames, extras, extranames,  :
>         invalid type (list) for variable 'tble[a]'
> >
>
>

-- 
Sarah Goslee
http://www.functionaldiversity.org