R help - Jun 2007 - Extracting lists in the dataframe $ format

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]'
> 

	[[alternative HTML version deleted]]

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

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.

I think your indexing is wrong in the function. Note
the tble[a] rather than tble[,a]. 

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



--- 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]'