[Rd] subscripting a terms object

[Martin Maechler]

Dear Terry,

>>>>> Therneau, Terry M , Ph D via R-devel 
>>>>>     on Thu, 4 Apr 2019 22:48:49 -0400 writes:

    > 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.)

The above two seem interesting and relevant to R itself.
As we've recently just fixed a buglet in  reformulate() --
probably unrelated to your problem --  I'd really be interested to see a
repr.ex. (reproducible example) for the above two statements.

... and if you want also a proposal on how to address the
problem in  delete.response()  and/or  `[.terms`()

Martin

    >  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.