[Rd] inconsistency or bug in coef() (PR#9358)

[ripley at stats.ox.ac.uk]

On Mon, 13 Nov 2006, rmh at temple.edu wrote:

> tmp <- data.frame(x=c(1,1),
>                  y=c(1,2))
>
> tmp.lm <- lm(y ~ x, data=tmp)
> summary(tmp.lm)
>
> coef(summary(tmp.lm))
>
> ## I consider this to be a bug.  Since summary(tmp.lm) gives
> ## two rows for the coefficients, I believe the coef() function
> ## should also give two rows.

That claim is false: it is print.summary.lm that is giving two lines, not 
the result of summary.lm: try

unclass(summary(tmp.lm))

This is also clear from the Value section of ?summary.lm, whose See Also 
says

      Function 'coef' will extract the matrix of coefficients with
      standard errors, t-statistics and p-values.

The point is that the print method is making use of both the $coefficients 
and the $aliased components.

I really do think this is clear from reading the help page: did you 
actually cross-check before sending a bug report?

>
>
>
>> summary(tmp.lm)
>
> Call:
> lm(formula = y ~ x, data = tmp)
>
> Residuals:
>   1    2
> -0.5  0.5
>
> Coefficients: (1 not defined because of singularities)
>            Estimate Std. Error t value Pr(>|t|)
> (Intercept)      1.5        0.5       3    0.205
> x                 NA         NA      NA       NA
>
> Residual standard error: 0.7071 on 1 degrees of freedom
>
>> coef(summary(tmp.lm))
>            Estimate Std. Error t value  Pr(>|t|)
> (Intercept)      1.5        0.5       3 0.2048328
>>
>> version
>               _
> platform       i386-pc-mingw32
> arch           i386
> os             mingw32
> system         i386, mingw32
> status
> major          2
> minor          4.0
> year           2006
> month          10
> day            03
> svn rev        39566
> language       R
> version.string R version 2.4.0 (2006-10-03)
>>
>
>
> ## this is a related problem
>
> tmp <- data.frame(x=c(1,2),
>                  y=c(1,2))
>
> tmp.lm <- lm(y ~ x, data=tmp)
> summary(tmp.lm)
>
> coef(summary(tmp.lm))
>
> ## Here the summary() give NA for the values that can't be
> ## calculated and the coef() function gives NaN.  I think both
> ## functions should return the same result.
>
>
>> summary(tmp.lm)
>
> Call:
> lm(formula = y ~ x, data = tmp)
>
> Residuals:
> ALL 2 residuals are 0: no residual degrees of freedom!
>
> Coefficients:
>            Estimate Std. Error t value Pr(>|t|)
> (Intercept)        0         NA      NA       NA
> x                  1         NA      NA       NA
>
> Residual standard error: NaN on 0 degrees of freedom
> Multiple R-Squared:     1,      Adjusted R-squared:   NaN
> F-statistic:   NaN on 1 and 0 DF,  p-value: NA
>
>>
>> coef(summary(tmp.lm))
>            Estimate Std. Error t value Pr(>|t|)
> (Intercept)        0        NaN     NaN      NaN
> x                  1        NaN     NaN      NaN
>>
>>
>
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>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595