[Rd] ** operator

[Roger Bivand]

On Thu, 15 May 2008, Barry Rowlingson wrote:

> Duncan Murdoch wrote:
>
>>  It's fairly unlikely to go away, but it's an old undocumented feature, so
>>  use at your own risk.  There are lots of other undocumented features, but
>>  maybe no others at the lexical level.  Check out src/main/gram.y if you
>>  want to search for more at that level, and src/* if you want them at any
>>  level.
>
>
> I just had a quick browse in the source and I can't see where "**" is 
> defined. names.c relates ^ to the power operation in arithmetic.c but no sign 
> of "**":
>
> ./names.c:{"^",         do_arith,       POWOP,  1,      2, {PP_BINARY2, 
> PREC_POWER,  1}},
>
> grepping for POWOP doesn't help.
>
>  It's not an operator like '*':
>>  get("**")
> Error in get("**") : variable "**" was not found
>>  get("*")
> function (e1, e2)  .Primitive("*")
>
> and there's no ** in gram.y.
>
> searching for 'power' and quoted "**" doesn't help me either. Searching for 
> unquoted ** just produces too much C code to be useful.
>
> It's got to be there somewhere!!!

Is there a clue in:

> "^"(5, 2)
[1] 25
> "**"(5, 2)
Error: could not find function "**"
> 5 ^ 2
[1] 25
> 5 ** 2
[1] 25

that is, it is truly obfuscated and not accessible using contemporary 
interfaces?

Roger

>
> Barry
>
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>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no