[Rd] as.Date (and strptime?) does not recognize "  " as a blank

[Spencer Graves]

Thanks, Prof. Ripley, for your further analysis of this issue.  sg


On 7/7/22 6:59 AM, Prof Brian Ripley wrote:
> There is some misunderstanding here.  The space is part of the format 
> specified by SG to as.Date(), which passes it to strptime(). So SG asked 
> to match a space and complained that a different character is not matched!
> 
> Reading the documentation of strptime shows
> 
>       ‘%n’ Newline on output, arbitrary whitespace on input.
>       ‘%t’ Tab on output, arbitrary whitespace on input.
> 
> so one might hope that one could use those to specify whitespace instead 
> of ASCII space in the format.  But unfortunately whether a Unicode 
> no-break space (U+00A0) is whitespace is a matter of opinion -- for 
> example the PCRE author changed his a few years back.
> 
> We don't have a reproducible example, but my attempt at reproduction 
> suggests that U+00A0 is not regarded as whitespace on the system I used. 
>   We know this to be platform-specific (it uses the C function 
> iswspace): glibc does not regard this as whitespace and the replacement 
> functions used by R on macOS and Windows have followed suit.
> 
> In short, ASCII space matches only itself, and the interpretation of 
> 'blank' (in regexps) or 'whitespace' (in strptime or regexps) is 
> platform-specific and liable to change.
> 
> 
> On 25/06/2022 14:13, Spencer Graves wrote:
>> Hi, Maxim et al.:
>>
>>
>> On 6/25/22 6:10 AM, Maxim Nazarov wrote:
>>> Hello,
>>>
>>>> When is a space not a space?
>>> I guess the answer is when it is a non-breaking one?..
>>>
>>> We can observe:
>>>   > charToRaw(textutils::HTMLdecode(" "))
>>>   [1] c2 a0
>>>   > charToRaw(" ")
>>>   [1] 20
>>> So one can argue that everything works correctly - `textutils` 
>>> function converts HTML's non-breaking space ' ' into R's 
>>> non-breaking space '\xa0', while %e format of as.Date expects a 
>>> 'normal' space.
>>> But this is obviously not user-friendly especially since both symbols 
>>> are displayed the same way on the console.
>>> So your options might be to either:
>>>   * manually change all 'weird' spaces into normal ones with 
>>> something like gsub("\\h", " ", ..., perl = TRUE) - for the list of 
>>> other weird spaces see 
>>> https://www.pcre.org/original/doc/html/pcrepattern.html#genericchartypes
>>>   * persuade textutils author to change   into a normal space 
>>> (they seem to be working with a simple lookup table - 
>>> https://github.com/enricoschumann/textutils/blob/b813c7bd4b55daef5fa7612e3fbfe82962711940/R/char_refs.R#L1465-L1466) 
>>>
>>>   * persuade R-Core (or submit a PR) to relax expectations of 
>>> as.Date/strptime
>>>
>>
>>        Thanks for the reply.  Since "this is obviously not 
>> user-friendly", as you noted, I felt a need to bring it to the 
>> attention of this group, and let them decide what if anything they 
>> would want to do about it.
>>
>>
>>        In any event, I found a fix for my immediate problem.  It's not 
>> as elegant as yours, but it works.
>>
>>        Best Wishes,
>>        Spencer
>>
>>
>>
>>
>>> Kind regards,
>>> Maxim Nazarov
>>>
>>> ----- On Jun 25, 2022, at 8:37 AM, Spencer Graves 
>>> spencer.graves using prodsyse.com wrote:
>>>
>>>> Hello, All:
>>>>
>>>>
>>>>       When is a space not a space?
>>>>
>>>>
>>>>       Consider the following:
>>>>
>>>>
>>>>> (pblmDate <- textutils::HTMLdecode(" 2 Mar 2018"))
>>>> [1] " 2 Mar 2018"
>>>>> as.Date(pblmDate, format='%e %b %Y')
>>>> [1] NA
>>>>> as.Date(' 2 Mar 2018', format='%e %b %Y')
>>>> [1] "2018-03-02"
>>>>
>>>>
>>>>       Is this a feature or a bug?
>>>>
>>>>
>>>>       I can work around it, now that I know what it is, but it took 
>>>> me a
>>>> few hours to diagnose.
>>>>
>>>>
>>>>       Thanks,
>>>>       Spencer Graves
>>>>
>>>>
>>>> p.s.  I got this from scraping a website with code that had worked for
>>>> me roughly 20 months ago.  I suspect that in the interim, someone
>>>> probably replaced ' 2 Mar 2018' with " 2 Mar 2018".
>>>>
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