[Rd] problem with glm (PR#452)

[Brad McNeney]

I looked into the glm problem some more. Seems to be a memory problem that
occurs just after garbage collection. The easiest way for me to
reproduce  the error is in lapply. I take a list and ask lapply to provide
the descriptive stat summary. I do this several times with the same list.
Most often it gives the correct summary, but just after allocSExp calls
R_gc, one of the summaries for a list element will be NULL. 

E.g for a data frame dat with five columns I get the following (having added
print statements in summary.default and in allocSExp just after the test
for whether gc is necessary):

> lapply(as.list(dat), summary, maxsum = maxsum)
[1] "exiting summary.default"
R_FreeSEXP == NULL  
[1] "exiting summary.default"
[1] "exiting summary.default"
[1] "exiting summary.default"
[1] "exiting summary.default"
$Delta
   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
   0.00    1.00    1.00    1.19    2.00    2.00 

$D
NULL

$R
   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
   0.00    1.00    1.00    0.86    1.00    1.00 

$V
    Min.  1st Qu.   Median     Mean  3rd Qu.     Max. 
0.004552 0.740700 1.575000 1.754000 3.205000 3.390000 

$X
   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
    0.0     0.0     0.5     0.5     1.0     1.0 


I don't know if the following is relevant, but for some reason I've found 
I can avoid this particular problem if I make a small change in lapply in 
its main loop.  Around line 50 of apply.c:

    PROTECT(ans = allocVector(VECSXP, n));
    for(i = 0; i < n; i++) {
        INTEGER(ind)[0] = i + 1;
        VECTOR(ans)[i] = eval(R_fcall, rho);
    }

if I change it to make an assignment to a
temporary variable first everything seems to work fine:

    PROTECT(ans = allocVector(VECSXP, n));
    for(i = 0; i < n; i++) {
        INTEGER(ind)[0] = i + 1;
        tem = eval(R_fcall, rho);
        VECTOR(ans)[i] = tem;
    }

hasn't given me any NULLs yet. 



On 20 Feb 2000, Peter Dalgaard BSA wrote:

> Brad McNeney <mcneney@cs.sfu.ca> writes:
> 
> > I'll see what I can do about getting a more reproducible error. 
> > 

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