[R] Can't understand error message :-{

[John Logsdon]

On 2 Mar 1999, Peter Dalgaard BSA wrote:

> 
> (1) Missing values in response and/or regressors cause cases to be
>     discarded. 
> (2) Plotting which of the y's against which x's ?
> 
> plot(mschmod$residuals ~ size94[complete.cases(mavgres,crimesch,
> socstat,povnojob,ploinc94,aa94,hisp94,minty94,mixed94)])
> 
> should do the trick. Or, simpler but sneakier:
> 
> attach(sizef[rownames(mschmod$model),])
> plot(residuals(mschmod) ~ size94)
> detach()
> 
> It should also work with:
> 
> evalq(plot(residuals(mschmod) ~ size94), sizef[rownames(mschmod$model),])
> 
> (none of the above is tested, since I don't have your data of course)

The problems of plotting residuals vs fitted data/covariates where there
are NAs caught me out a little while ago.  Would it not be better if the
fitting functions lm, glm etc and plot were consistent?  Thus either (a)
plot() omitted cases in the X or the Y which were NA before checking for
length consistency or (b) residuals() etc included NA in the appropriate
places. 

Another consequence of the present inconsistency is that, it *is* possible
that the vector contraction just happens to return a vector of the same
length.  This happened to me without realising it for a time - I had 625
items and took a subset of 620 but, through ignorance of the correct
commands and a good measure of stupidity, it was the wrong subset! 
Fortunately I checked and from the plots it was obvious that something was
wrong but it makes me rather nervous when handling big data sets.  Mea
culpa I know but it is an easy trap to fall into. 

Where there are lots of NA's and lots of subsets of data, I also find
myself making too many similar copies of data to avoid very long plot() 
commands then forgetting which is which.  Another case for an extended
form of ls() (ls-l maybe) as recently suggested which includes the
structure size and perhaps class etc.

John

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