[Rd] subscripting a terms object

[Therneau, Terry M., Ph.D.]

Someone sent me a bug report for survival2.44.1-1 that involves a model with both cluster 
and offset.  It turns out to be a 3 part issue with [.terms and my own untangle.specials 
routine.   I've spent an evening sorting out the details.


   1. The delete.response() function doesn't remove the response from the dataClasses 
attribute, which leads to a later failure in [.terms for no-response models.  Is there a 
reason for this, or can I make my patch include this oversight as well?

  2. [.terms messes up predvars and dataClasses if the model has an offset term in it.  
(In select cases 1 and 2 can cancel out and give the correct dataClasses attribute.)

  3. The survival::untangle.specials routine assumed that you can use the same 
subscripting for the terms of a model and the term() object itself, which turns out to be 
almost always true, but only almost.

   The failure turns out to have probably been there since the Splus days, which tells one 
just how often such a model is used. (One of two edge case bugs sent to me in the first 
days after I pushed it to CRAN: a new release seems to attact them.)   I'm willing to put 
together a patch, but given the rarity of these would folks prefer to wait until after the 
April release?   I'm fine with that.  I need the answer to 1 though.

Terry T.


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