[Rd] as.matrix.Surv -- R core question/opinions

Terry Therneau therneau at mayo.edu
Thu Dec 6 15:48:13 CET 2012

1. A Surv object is a matrix with some extra attributes.  The as.matrix.Surv function 
removes the extras but otherwise leaves it as is.

2. The last several versions of the survival library were accidentally missing the 
S3method('as.matrix', 'Surv') line from their NAMESPACE file.  (Instead it's position is 
held by a duplicate of the line just above it in the NAMESPACE file, suggesting a 
copy/paste error).  As a consequence the as.matrix.Surv function was effectively ignored, 
and the default method was being used.
    The as.matrix.default function leaves anything with a "dim" attribute alone.

3. In my current about-to-submit-to-CRAN  version of survival the missing NAMESPACE line 
was restored.  This breaks one function in one package (rms) which calls "as.matrix(y)" on 
a Surv object but then later looks at the "type" attribute of y.

  So now to the design question: should the as.matrix.Surv function "sanitize" the result 
by removing the extra attributes, or should it leave them alone?  The first seems cleaner; 
my accidental multi-year test of leaving them in, however, clearly shows that it does no 

Terry T.

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