[Rd] Limitation of dirname() and basename()

[Herve Pages]

Hi,

Simon Urbanek wrote:
> Your proposed behavior is inconsistent, anyway. The purpose of  
> dirname is to return parent directory of the entity represented by  
> the pathname.

Mmmm, I don't think this is true:

  > dirname("aaa/..")
  [1] "aaa"

"aaa" is not the parent directory of "aaa/.."

Same here:

  > dirname("/usr/./.")
  [1] "/usr/."


> "/my/path" and "/my/path/" are equivalent as they both  
> represent the directory "path" whose parent is "/my", therefore  
> returning "/my/path" in either case is inconsistent with the purpose  
> of this function. As of trailing slashes (independently of dirname),  
> sadly, some programs exploit the equivalence of both representations  
> by encoding meta-information in the representation, but this behavior  
> is quite confusing and error-prone. You're free to add such special  
> cases to your application, but there is no reason to add such  
> confusion to R.

Note that Python's designers were not afraid to emancipate from Unix for
this particular case:

  >>> import os.path
  >>> os.path.dirname("aaa/..")
  'aaa'
  >>> os.path.dirname("aaa/../")
  'aaa/..'


Also note that, if the goal was to mimic Unix behaviour, then why not
fully go for it, even for edge-cases:

  R
  ----
  > dirname("/")
  [1] "/"
  > basename("/")
  [1] ""

  Unix
  ----
  hpages at lamb1:~> dirname "/"
  /
  hpages at lamb1:~> basename "/"
  /

Just my 2 cents...

Cheers,
H.


> 
> Cheers,
> Simon
> 
> 
> 
>>>> Prof Brian Ripley wrote:
>>>>> These functions work as they should: did you not read the help page
>>>>> which explicitly tells you what happens in this case?
>>>>>
>>>>> The Unix originals work in the same way:
>>>>>
>>>>> gannet% dirname /my/path/
>>>>> /my
>>>>>
>>>>> Please DO study the R posting guide and do the homework requesting
>>>>> of you before posting.
>>>>>
>>>>> On Mon, 26 Mar 2007, cstrato wrote:
>>>>>
>>>>>> Dear all,
>>>>>>
>>>>>> I have already twice encountered a case which I consider a
>>>>>> limitation of
>>>>>> dirname() and basename().
>>>>>>
>>>>>> In my functions I have a parameter "outfile" which e.g. tells  
>>>>>> where
>>>>>> a file
>>>>>> should be stored. Usually "outfile" is of the form:
>>>>>> oufile = "/my/path/myname.txt"
>>>>>>
>>>>>>> outfile <- "/my/path/myname.txt"
>>>>>>> dirname(outfile)
>>>>>> [1] "/my/path"
>>>>>>> basename(outfile)
>>>>>> [1] "myname.txt"
>>>>>>
>>>>>> However, in addition I want to be able to define the path only,  
>>>>>> while
>>>>>> creating the name "myname.txt" automatically.
>>>>>> Sorrowly, I get the following:
>>>>>>
>>>>>>> outfile <- "/my/path/"
>>>>>>> dirname(outfile)
>>>>>> [1] "/my"
>>>>>>> basename(outfile)
>>>>>> [1] "path"
>>>>>>
>>>>>> It would be great if dirname() and basename() could recognize:
>>>>>> dirname("/my/path/")      = /my/path/
>>>>>> basename(""/my/path/")  = ""
>>>>>> i.e. they should be able to recognize a trailing "/".
>>>>> Not according to the documentation.
>>>>>
>>>>>> Best regards
>>>>>> Christian
>>>>>> _._._._._._._._._._._._._._._._
>>>>>> C.h.i.s.t.i.a.n S.t.r.a.t.o.w.a
>>>>>> V.i.e.n.n.a       A.u.s.t.r.i.a
>>>>>> _._._._._._._._._._._._._._._._
>>>> ______________________________________________
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>>>
>>>
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> 
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