[Rd] integer coercion when indexing and subsetting (PR#2430)

[maechler@stat.math.ethz.ch]

At the end of his bug report, Philippe says

    PhGr> ..... Moreover, the subset operation [] uses as.integer() and
    PhGr> consequently, can suffer from the same syndrome. A WARNING section in
    PhGr> Extract.Rd would be welcome too.

[BTW: Thank you Philippe! ]

Currently, "Extract.Rd" does not say anything on the kind of
indices `i' that can be used in things like x[i].

OTOH, the R language reference has a nice section

>>    Indexing by vectors
>>    -------------------
>>      R allows some powerful constructions using vectors as indices.  We
>>   shall discuss indexing of simple vectors first.  For simplicity, assume
>>   that the expression is `x[i]'.  Then the following possibilities exist
>>   according to the type of `i'.
>> 
>>      *Integer* ...............
>>      ........................    
>> 
>> 
>>      * *Other numeric*.  Non-integer values are converted to integer
>>        before use.
>> 
>>       <<........>>

I agree with Philippe that  help(Extract) should say more.

1) point to the "R Language Reference"

  BTW: we should think on how to do this with links that work
     with HTML/PDF and also with ESS and Info (I read all R
      manuals in info most of the time).
    
  For the moment, just could use \url{....}, right?

2) Tell about `i' = names or integers or as.integer(numeric)
   at least, right?


Martin Maechler <maechler@stat.math.ethz.ch>	http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum  LEO C16	Leonhardstr. 27
ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
phone: x-41-1-632-3408		fax: ...-1228			<><