Re: [R] Flummoxed by gsub().

[David Winsemius]

> On Aug 24, 2017, at 10:20 AM, David Winsemius  wrote:
> 
> 
>> On Aug 23, 2017, at 2:29 AM, Rolf Turner  wrote:
>> 
>> 
>> On 23/08/17 18:33, Stefan Evert wrote:
>> 
 On 23 Aug 2017, at 07:45, Rolf Turner  wrote:
 
 My reading of ?regex led me to believe that
 
   gsub("[:alpha:]","",x)
 
 should give the result that I want.
>>> That's looking for any of the characters a, l, p, h, : .
>> 
>> OK.  I see that now.  I don't think that it's really stated anywhere that to 
>> search for (and possibly change) any one of a string of characters you 
>> enclose that string of characters in brackets [  ].
> 
> That's explained on the ?regex page in the section on character classes. The 
> source of confusion for you is that within regex character classes there is 
> also a set of reserved constructions that all start and end with "[:" and 
> ":]". It's a bit like needed to double or triple escape characters in regex. 
> a leading "|" changes the parser settings (or "expectations" if one wants to 
> anthropomorphize the process.

I meant a leading backslash "\" rather than a vertical bar ("|")

-- 
David.
> 
>> 
>> The first example from ?grep makes this "clear" (for some value of the word 
>> "clear") once you understand what this example is on about.
>> 
>> So it's "obvious" once you've been shown, and totally opaque until then.
> 
> Sometimes we all stumble over syntactic "special" detours. If you wanted to 
> add a warning to the current ?regex tex, you could submit a diff for the base 
> package, perhaps with something like:
> 
> "Certain named classes of characters are predefined. Their interpretation 
> depends on the locale (see locales); the interpretation below is that of the 
> POSIX locale."
> 
> Replaced with:
> 
> "Certain named classes of characters are predefined. Their interpretation 
> depends on the locale (see locales); the interpretation below is that of the 
> POSIX locale. Their names do include the "[:" and ":]" characters."
> 
> 
>> 
>>> What you meant to say was
>>> gsub("[[:alpha:]]","",x)
>>> i.e. the character class [:alpha:] within a character set.
>> 
>> Yup.  Got it.  Thanks very much.
>> 

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Re: [R] Flummoxed by gsub().

[David Winsemius]

> On Aug 23, 2017, at 2:29 AM, Rolf Turner  wrote:
> 
> 
> On 23/08/17 18:33, Stefan Evert wrote:
> 
>>> On 23 Aug 2017, at 07:45, Rolf Turner  wrote:
>>> 
>>> My reading of ?regex led me to believe that
>>> 
>>>gsub("[:alpha:]","",x)
>>> 
>>> should give the result that I want.
>> That's looking for any of the characters a, l, p, h, : .
> 
> OK.  I see that now.  I don't think that it's really stated anywhere that to 
> search for (and possibly change) any one of a string of characters you 
> enclose that string of characters in brackets [  ].

That's explained on the ?regex page in the section on character classes. The 
source of confusion for you is that within regex character classes there is 
also a set of reserved constructions that all start and end with "[:" and ":]". 
It's a bit like needed to double or triple escape characters in regex. a 
leading "|" changes the parser settings (or "expectations" if one wants to 
anthropomorphize the process.

> 
> The first example from ?grep makes this "clear" (for some value of the word 
> "clear") once you understand what this example is on about.
> 
> So it's "obvious" once you've been shown, and totally opaque until then.

Sometimes we all stumble over syntactic "special" detours. If you wanted to add 
a warning to the current ?regex tex, you could submit a diff for the base 
package, perhaps with something like:

"Certain named classes of characters are predefined. Their interpretation 
depends on the locale (see locales); the interpretation below is that of the 
POSIX locale."

Replaced with:

"Certain named classes of characters are predefined. Their interpretation 
depends on the locale (see locales); the interpretation below is that of the 
POSIX locale. Their names do include the "[:" and ":]" characters."


> 
>> What you meant to say was
>>  gsub("[[:alpha:]]","",x)
>> i.e. the character class [:alpha:] within a character set.
> 
> Yup.  Got it.  Thanks very much.
> 
> cheers,
> 
> Rolf
> 
> -- 
> Technical Editor ANZJS
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
> 
> __
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius
Alameda, CA, USA

'Any technology distinguishable from magic is insufficiently advanced.'   
-Gehm's Corollary to Clarke's Third Law

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Re: [R] Flummoxed by gsub().

[William Dunlap via R-help]

Note that the "doubled brackets" are not essential to this usage.
[:characterClass:] is recognized inside of square brackets as a shortcut
for listing a bunch of characters.  You can mix it with other characters or
character classes inside a set of square brackets.

E.g., the following pattern matches letters, digits, and the dollar and
percent signs.

> gsub("[$[:alpha:]%[:digit:]]", "-", c("$6 is 50% of $12.00"))
[1] "-- -- --- -- ---.--"


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Wed, Aug 23, 2017 at 3:39 PM, Rolf Turner 
wrote:

> On 24/08/17 02:46, Bert Gunter wrote:
>
>> Inline.
>>
>> -- Bert
>>
>>
>> Bert Gunter
>>
>> "The trouble with having an open mind is that people keep coming along
>> and sticking things into it."
>> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
>>
>>
>> On Wed, Aug 23, 2017 at 2:29 AM, Rolf Turner 
>> wrote:
>>
>>>
>>> On 23/08/17 18:33, Stefan Evert wrote:
>>>
>>>
 On 23 Aug 2017, at 07:45, Rolf Turner  wrote:
>
> My reading of ?regex led me to believe that
>
>  gsub("[:alpha:]","",x)
>
> should give the result that I want.
>


 That's looking for any of the characters a, l, p, h, : .

>>>
>>>
>>> OK.  I see that now.  I don't think that it's really stated anywhere
>>> that to
>>> search for (and possibly change) any one of a string of characters you
>>> enclose that string of characters in brackets [  ].
>>>
>>> The first example from ?grep makes this "clear" (for some value of the
>>> word
>>> "clear") once you understand what this example is on about.
>>>
>>> So it's "obvious" once you've been shown, and totally opaque until then.
>>>
>>
>> Well, "obviousness" is in the mind of the beholder, but, from ?regexp:
>>
>> "A character class is a list of characters enclosed between [ and ]
>> which matches any single character in that list; "... (at the end of
>> the above section)
>>
>> "For example, [[:alnum:]] means [0-9A-Za-z] "...
>>
>> Note the doubled brackets. So seems pretty explicit to me.
>>
>
> Well, yes.  Once it's pointed out it's "obvious".  But it's buried pretty
> deeply in a large mass of text, and I didn't see it until you pointed it
> out.
>
> If *I* had written the help file, it would be much more perspicuous.
>
> cheers,
>
> Rolf
>
> --
> Technical Editor ANZJS
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
>
> __
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posti
> ng-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

[[alternative HTML version deleted]]

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Re: [R] Flummoxed by gsub().

[Rolf Turner]

On 24/08/17 02:46, Bert Gunter wrote:

Inline.

-- Bert


Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Wed, Aug 23, 2017 at 2:29 AM, Rolf Turner  wrote:


On 23/08/17 18:33, Stefan Evert wrote:




On 23 Aug 2017, at 07:45, Rolf Turner  wrote:

My reading of ?regex led me to believe that

 gsub("[:alpha:]","",x)

should give the result that I want.



That's looking for any of the characters a, l, p, h, : .



OK.  I see that now.  I don't think that it's really stated anywhere that to
search for (and possibly change) any one of a string of characters you
enclose that string of characters in brackets [  ].

The first example from ?grep makes this "clear" (for some value of the word
"clear") once you understand what this example is on about.

So it's "obvious" once you've been shown, and totally opaque until then.


Well, "obviousness" is in the mind of the beholder, but, from ?regexp:

"A character class is a list of characters enclosed between [ and ]
which matches any single character in that list; "... (at the end of
the above section)

"For example, [[:alnum:]] means [0-9A-Za-z] "...

Note the doubled brackets. So seems pretty explicit to me.


Well, yes.  Once it's pointed out it's "obvious".  But it's buried 
pretty deeply in a large mass of text, and I didn't see it until you 
pointed it out.


If *I* had written the help file, it would be much more perspicuous.

cheers,

Rolf

--
Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276

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Re: [R] Flummoxed by gsub().

[Bert Gunter]

Inline.

-- Bert


Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Wed, Aug 23, 2017 at 2:29 AM, Rolf Turner  wrote:
>
> On 23/08/17 18:33, Stefan Evert wrote:
>
>>
>>> On 23 Aug 2017, at 07:45, Rolf Turner  wrote:
>>>
>>> My reading of ?regex led me to believe that
>>>
>>> gsub("[:alpha:]","",x)
>>>
>>> should give the result that I want.
>>
>>
>> That's looking for any of the characters a, l, p, h, : .
>
>
> OK.  I see that now.  I don't think that it's really stated anywhere that to
> search for (and possibly change) any one of a string of characters you
> enclose that string of characters in brackets [  ].
>
> The first example from ?grep makes this "clear" (for some value of the word
> "clear") once you understand what this example is on about.
>
> So it's "obvious" once you've been shown, and totally opaque until then.

Well, "obviousness" is in the mind of the beholder, but, from ?regexp:

"A character class is a list of characters enclosed between [ and ]
which matches any single character in that list; "... (at the end of
the above section)

"For example, [[:alnum:]] means [0-9A-Za-z] "...

Note the doubled brackets. So seems pretty explicit to me.

Cheers,
Bert





>
>> What you meant to say was
>>
>> gsub("[[:alpha:]]","",x)
>>
>> i.e. the character class [:alpha:] within a character set.
>
>
> Yup.  Got it.  Thanks very much.
>
> cheers,
>
> Rolf
>
> --
> Technical Editor ANZJS
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
>
> __
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

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Re: [R] Flummoxed by gsub().

[Rolf Turner]

On 23/08/17 18:41, PIKAL Petr wrote:

Hi Rolf

I am not at all an expert in regex but

gsub("[[:alpha:]]","",x)

Works as you expected. Do not ask me why.


Thanks Petr.  Stefan Evert's explanation clarified the issue.  Which I 
must say *needed* some clarification!


cheers,

Rolf

--
Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276

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Re: [R] Flummoxed by gsub().

[Rolf Turner]

On 23/08/17 18:33, Stefan Evert wrote:




On 23 Aug 2017, at 07:45, Rolf Turner  wrote:

My reading of ?regex led me to believe that

gsub("[:alpha:]","",x)

should give the result that I want.


That's looking for any of the characters a, l, p, h, : .


OK.  I see that now.  I don't think that it's really stated anywhere 
that to search for (and possibly change) any one of a string of 
characters you enclose that string of characters in brackets [  ].


The first example from ?grep makes this "clear" (for some value of the 
word "clear") once you understand what this example is on about.


So it's "obvious" once you've been shown, and totally opaque until then.


What you meant to say was

gsub("[[:alpha:]]","",x)

i.e. the character class [:alpha:] within a character set.


Yup.  Got it.  Thanks very much.

cheers,

Rolf

--
Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276

__
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Re: [R] Flummoxed by gsub().

[PIKAL Petr]

Hi Rolf

I am not at all an expert in regex but

gsub("[[:alpha:]]","",x)

Works as you expected. Do not ask me why.

Cheers
Petr


> -Original Message-
> From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Rolf Turner
> Sent: Wednesday, August 23, 2017 7:46 AM
> To: r-help mailing list <r-help@r-project.org>
> Subject: [R] Flummoxed by gsub().
>
>
> I have a vector (say "x") of the form
>
>  [1] "mung5"  "mung10" "mung20" "gorp5"  "gorp10" "gorp20"
>
> I want to extract just the numbers (strings of digits) that appear at the end 
> of
> the strings in "x".
>
> My reading of ?regex led me to believe that
>
>  gsub("[:alpha:]","",x)
>
> should give the result that I want.  However it returns
>
>  [1] "mung5"  "mung10" "mung20" "gor5"   "gor10"  "gor20"
>
> i.e. it chops the last letter out of the "gorp" string, but nothing else.
>
> I am completely bewildered by this behaviour and can see no rationale for it
> nor any way to adjust my syntax to get what I want.
>
> A bit of Googling led me to the information that
>
>  gsub("\\D","",x)
>
> should work, and indeed it does, giving:
>
>  [1] "5"  "10" "20" "5"  "10" "20"
>
> OM!  (Apparently "\D" means *not* a digit.)
>
> So I have *a* solution to my problem.  However I would really like to know why
> the  the first idea I tried did not work and what it is 
> actually
> *doing*!
>
> Anybody?
>
> cheers,
>
> Rolf Turner
>
> --
> Technical Editor ANZJS
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
>
> __
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.


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Re: [R] Flummoxed by gsub().

[Stefan Evert]

> On 23 Aug 2017, at 07:45, Rolf Turner  wrote:
> 
> My reading of ?regex led me to believe that
> 
>gsub("[:alpha:]","",x)
> 
> should give the result that I want. 

That's looking for any of the characters a, l, p, h, : .

What you meant to say was

gsub("[[:alpha:]]","",x)

i.e. the character class [:alpha:] within a character set.

Best,
Stefan

__
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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[R] Flummoxed by gsub().

[Rolf Turner]

I have a vector (say "x") of the form

[1] "mung5"  "mung10" "mung20" "gorp5"  "gorp10" "gorp20"

I want to extract just the numbers (strings of digits) that appear at 
the end of the strings in "x".


My reading of ?regex led me to believe that

gsub("[:alpha:]","",x)

should give the result that I want.  However it returns

[1] "mung5"  "mung10" "mung20" "gor5"   "gor10"  "gor20"

i.e. it chops the last letter out of the "gorp" string, but nothing else.

I am completely bewildered by this behaviour and can see no rationale 
for it nor any way to adjust my syntax to get what I want.


A bit of Googling led me to the information that

gsub("\\D","",x)

should work, and indeed it does, giving:

[1] "5"  "10" "20" "5"  "10" "20"

OM!  (Apparently "\D" means *not* a digit.)

So I have *a* solution to my problem.  However I would really like to 
know why the  the first idea I tried did not work and

what it is actually *doing*!

Anybody?

cheers,

Rolf Turner

--
Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276

__
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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