[R] sub question

[Gabor Grothendieck]

On Sat, Jan 31, 2009 at 6:01 PM, Wacek Kusnierczyk
<Waclaw.Marcin.Kusnierczyk at idi.ntnu.no> wrote:
> Gabor Grothendieck wrote:
>> On Sat, Jan 31, 2009 at 4:46 PM, Wacek Kusnierczyk
>> <Waclaw.Marcin.Kusnierczyk at idi.ntnu.no> wrote:
>>
>>> David Hajage wrote:
>>>
>>>> Thank you, it's perfect.
>>>>
>>>>
>>> to extend the context, if you were to solve the problem in perl, the
>>> regex below would work in perl 5.10, but not in earlier versions of
>>> perl;  another approach is to replace the unwanted leading characters
>>> with equally many replacement characters at once.
>>>
>>> $string = 'aabaab';
>>>
>>> # perl 5.10
>>> $string =~ s/a|(*COMMIT)(*FAIL)/c/g
>>> # $string is 'ccbaab'
>>>
>>> # any recent perl
>>> $string =~ s/^a*/'c' x length $&/e;
>>> # $string is 'ccbaab'
>>>
>>> i don't know how (if) the latter could be done in r.
>>>
>>
>> This seems quite analogous:
>>
>> library(gsubfn)
>> s <- "aabaab"
>> gsubfn("^a*", ~ paste(rep("c", nchar(x)), collapse = ""), s)[[1]]
>>
>
> indeed, as does the following variant:
>
> gsubfn("^a*", ~ gsub(".", "c", x), s)[[1]]
>
>
> with some additional boring pedantry wrt. ?gsubfn, which says:
>
> " If 'replacement' is a formula instead of a function then a one
>     line function is created whose body is the right hand side of the
>     formula and whose arguments are the left hand side separated by
>     '+' signs (or any other valid operator).  The environment of the
>     function is the environment of the formula.  If the arguments are
>     omitted then the free variables found on the right hand side are
>     used in the order encountered.  "
>
> to my little mind, all of 'paste', 'rep', 'nchar', and 'x' in the
> example above are *free variables* on the right of the formula.  you

The first three are functions, not variables.