# \[bug\] String#split returns extra empty string **URL:** \ **Category:** ruby-talk\ **Created:** [31 May 2004 07:44 UTC](https://rubytalk.org/t/bug-string-split-returns-extra-empty-string/11833 "2004-05-31T07:44:31Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Simon\_Strandgaard1](https://avatars.discourse-cdn.com/v4/letter/s/e47c2d/32.png) [@Simon\_Strandgaard1](https://rubytalk.org/u/Simon_Strandgaard1)\ **Post date:** [31 May 2004 07:44 UTC](https://rubytalk.org/t/bug-string-split-returns-extra-empty-string/11833/1 "2004-05-31T07:44:31Z")
While extending my own regexp-engine with a split method, I discovered something odd about Ruby’s split. irb(main):001:0\> ‘ab1ab’.split(/\D+/) =\> ["", “1”] Its asymmetric, it has a special case for eliminating the last empty string… but apparently not the first empty string. I would have expected above to be symmetric, and output: =\> [“1”] > **···** > > – > Simon Strandgaard ---
**Author:** ![Simon\_Strandgaard1](https://avatars.discourse-cdn.com/v4/letter/s/e47c2d/32.png) [@Simon\_Strandgaard1](https://rubytalk.org/u/Simon_Strandgaard1)\ **Post date:** [31 May 2004 08:46 UTC](https://rubytalk.org/t/bug-string-split-returns-extra-empty-string/11833/2 "2004-05-31T08:46:22Z")
Simon Strandgaard wrote: > While extending my own regexp-engine with a split method, > I discovered something odd about Ruby’s split. > > irb(main):001:0\> ‘ab1ab’.split(/\D+/) > =\> [“”, “1”] > > Its asymmetric, it has a special case for eliminating > the last empty string… but apparently not the first empty string. > > I would have expected above to be symmetric, and output: > =\> [“1”] [10 minutes of experimenting later] I wasn’t aware that Ruby inserts subcaptures this way. irb(main):001:0\> “ab2cd3”.split(/(\D+)/, 2) =\> [“”, “ab”, “2cd3”] Because of subcapture insertion, it make sense to keep the first empty string. I withdraw this bug-report. > **···** > > – > Simon Strandgaard ---
**Author:** ![Robert](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@Robert](https://rubytalk.org/u/Robert)\ **Post date:** [31 May 2004 12:03 UTC](https://rubytalk.org/t/bug-string-split-returns-extra-empty-string/11833/3 "2004-05-31T12:03:37Z")
“Simon Strandgaard” [neoneye@adslhome.dk](mailto:neoneye@adslhome.dk) schrieb im Newsbeitrag news:20040531104155.074a42b0.neoneye@adslhome.dk… > Simon Strandgaard wrote: > > > While extending my own regexp-engine with a split method, > > I discovered something odd about Ruby’s split. > > > > irb(main):001:0\> ‘ab1ab’.split(/\D+/) > > =\> [“”, “1”] > > > > Its asymmetric, it has a special case for eliminating > > the last empty string… but apparently not the first empty string. > > > > I would have expected above to be symmetric, and output: > > =\> [“1”] > > [10 minutes of experimenting later] > I wasn’t aware that Ruby inserts subcaptures this way. > > irb(main):001:0\> “ab2cd3”.split(/(\D+)/, 2) > =\> [“”, “ab”, “2cd3”] > > Because of subcapture insertion, it make sense to keep the > first empty string. > > I withdraw this bug-report. But what about: > > ‘ab’.split(/\D+/) > > =\> You would at least expect one empty string in the result since there is at least one separator. This strikes me as odd. ``` robert ``` ---
**Author:** ![Simon\_Strandgaard1](https://avatars.discourse-cdn.com/v4/letter/s/e47c2d/32.png) [@Simon\_Strandgaard1](https://rubytalk.org/u/Simon_Strandgaard1)\ **Post date:** [31 May 2004 12:09 UTC](https://rubytalk.org/t/bug-string-split-returns-extra-empty-string/11833/4 "2004-05-31T12:09:19Z")
Guy Decoux very recently explained that to me. When split has no limit, it wipes empty strings. In your case you would have expected it to output [“”]… but because its an empty-string in the tail… it gets wiped. def split(pattern, limit=0) … unless limit # lets wipe tailing elements which are empty result.pop while result.size \> 0 and result.last.empty? end result end > **···** > > “Robert Klemme” [bob.news@gmx.net](mailto:bob.news@gmx.net) wrote: > > > “Simon Strandgaard” [neoneye@adslhome.dk](mailto:neoneye@adslhome.dk) schrieb im Newsbeitrag > > news:20040531104155.074a42b0.neoneye@adslhome.dk… > > > > > Simon Strandgaard wrote: > > > > > > > While extending my own regexp-engine with a split method, > > > > I discovered something odd about Ruby’s split. > > > > > > > > irb(main):001:0\> ‘ab1ab’.split(/\D+/) > > > > =\> [“”, “1”] > > > > > > > > Its asymmetric, it has a special case for eliminating > > > > the last empty string… but apparently not the first empty string. > > > > > > > > I would have expected above to be symmetric, and output: > > > > =\> [“1”] > > > > > > [10 minutes of experimenting later] > > > I wasn’t aware that Ruby inserts subcaptures this way. > > > > > > irb(main):001:0\> “ab2cd3”.split(/(\D+)/, 2) > > > =\> [“”, “ab”, “2cd3”] > > > > > > Because of subcapture insertion, it make sense to keep the > > > first empty string. > > > > > > I withdraw this bug-report. > > > > But what about: > > > > > > ‘ab’.split(/\D+/) > > > > =\> > > > > You would at least expect one empty string in the result since there is at > > least one separator. This strikes me as odd. > > – > Simon Strandgaard ---
**Author:** ![Robert](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@Robert](https://rubytalk.org/u/Robert)\ **Post date:** [31 May 2004 20:58 UTC](https://rubytalk.org/t/bug-string-split-returns-extra-empty-string/11833/5 "2004-05-31T20:58:40Z")
“Simon Strandgaard” [neoneye@adslhome.dk](mailto:neoneye@adslhome.dk) schrieb im Newsbeitrag news:20040531140451.3abb4fb2.neoneye@adslhome.dk… > > “Simon Strandgaard” [neoneye@adslhome.dk](mailto:neoneye@adslhome.dk) schrieb im Newsbeitrag > > news:20040531104155.074a42b0.neoneye@adslhome.dk… > > > > > Simon Strandgaard wrote: > > > > > > > While extending my own regexp-engine with a split method, > > > > I discovered something odd about Ruby’s split. > > > > > > > > irb(main):001:0\> ‘ab1ab’.split(/\D+/) > > > > =\> [“”, “1”] > > > > > > > > Its asymmetric, it has a special case for eliminating > > > > the last empty string… but apparently not the first empty string. > > > > > > > > I would have expected above to be symmetric, and output: > > > > =\> [“1”] > > > > > > [10 minutes of experimenting later] > > > I wasn’t aware that Ruby inserts subcaptures this way. > > > > > > irb(main):001:0\> “ab2cd3”.split(/(\D+)/, 2) > > > =\> [“”, “ab”, “2cd3”] > > > > > > Because of subcapture insertion, it make sense to keep the > > > first empty string. > > > > > > I withdraw this bug-report. > > > > But what about: > > > > > > ‘ab’.split(/\D+/) > > > > =\> > > > > You would at least expect one empty string in the result since there is > > at > > least one separator. This strikes me as odd. > > Guy Decoux very recently explained that to me. > > When split has no limit, it wipes empty strings. > > In your case you would have expected it to output [“”]… but > because its an empty-string in the tail… it gets wiped. > > def split(pattern, limit=0) > … > unless limit # lets wipe tailing elements which are empty > result.pop while result.size \> 0 and result.last.empty? > end > result > end But I though it will strip trailing empty strings - what about the leading empty string in my example? I’d expect that to be preserved. Hm… ``` robert ``` > **···** > > > “Robert Klemme” [bob.news@gmx.net](mailto:bob.news@gmx.net) wrote: ---
**Author:** ![Simon\_Strandgaard1](https://avatars.discourse-cdn.com/v4/letter/s/e47c2d/32.png) [@Simon\_Strandgaard1](https://rubytalk.org/u/Simon_Strandgaard1)\ **Post date:** [31 May 2004 22:48 UTC](https://rubytalk.org/t/bug-string-split-returns-extra-empty-string/11833/6 "2004-05-31T22:48:24Z")
Robert Klemme wrote: > But I though it will strip trailing empty strings - what about the leading > empty string in my example? I’d expect that to be preserved. Let take another example both with leading and tailing empty strings. irb(main):005:0\> ‘34ab34’.split(/\d+/, 10) =\> [“”, “ab”, “”] irb(main):006:0\> ‘34ab34’.split(/\d+/) =\> [“”, “ab”] When no limit are specified, Ruby wipes the tailing empty strings, until it reaches a non-empty string. In your case there are zero non-empty strings… so Ruby wipes everything. irb(main):001:0\> ‘ab’.split(/\D+/) =\> irb(main):002:0\> ‘ab’.split(/\D+/, 10) =\> [“”, “”] FYI: I have no idea when this wiping empty tail elements are useful. Any ideas ? > **···** > > – > Simon Strandgaard ---
**Author:** ![David\_A\_Black3](https://avatars.discourse-cdn.com/v4/letter/d/6a8cbe/32.png) [@David\_A\_Black3](https://rubytalk.org/u/David_A_Black3)\ **Post date:** [1 June 2004 03:23 UTC](https://rubytalk.org/t/bug-string-split-returns-extra-empty-string/11833/7 "2004-06-01T03:23:43Z")
Hi – Simon Strandgaard [neoneye@adslhome.dk](mailto:neoneye@adslhome.dk) writes: > FYI: I have no idea when this wiping empty tail elements are useful. > Any ideas ? Maybe a case like: irb(main):006:0\> "one two three “.split(” ") =\> [“one”, “two”, “three”] (though there you don’t need an argument to split at all I guess) or something like: irb(main):016:0\> “one!two!three!”.split(“!”) =\> [“one”, “two”, “three”] David > **···** > > – > David A. Black > [dblack@wobblini.net](mailto:dblack@wobblini.net) ---
**Author:** ![Florian\_Gross](https://avatars.discourse-cdn.com/v4/letter/f/e9a140/32.png) [@Florian\_Gross](https://rubytalk.org/u/Florian_Gross)\ **Post date:** [1 June 2004 13:28 UTC](https://rubytalk.org/t/bug-string-split-returns-extra-empty-string/11833/8 "2004-06-01T13:28:38Z")
David Alan Black wrote: > Hi – Moin! > > FYI: I have no idea when this wiping empty tail elements are useful. > > Any ideas ? > > Maybe a case like: > > irb(main):006:0\> "one two three “.split(” ") > =\> [“one”, “two”, “three”] > > (though there you don’t need an argument to split at all I guess) or > something like: > > irb(main):016:0\> “one!two!three!”.split(“!”) > =\> [“one”, “two”, “three”] Hm, I think that it causes more trouble than it’s worth. It’s very easy to remove empty elements anyway: ``` "one!two!three!".split("!").reject { |item| item.empty? } ``` Maybe it would be better to create a reject\_at\_end/at\_start or something similar? Regards, Florian Gross ---
**Author:** ![David\_A\_Black3](https://avatars.discourse-cdn.com/v4/letter/d/6a8cbe/32.png) [@David\_A\_Black3](https://rubytalk.org/u/David_A_Black3)\ **Post date:** [1 June 2004 13:52 UTC](https://rubytalk.org/t/bug-string-split-returns-extra-empty-string/11833/9 "2004-06-01T13:52:51Z")
Hi – > David Alan Black wrote: > > > Hi – > > Moin! > > > > FYI: I have no idea when this wiping empty tail elements are useful. > > > Any ideas ? > > > > Maybe a case like: > > > > irb(main):006:0\> "one two three “.split(” ") > > =\> [“one”, “two”, “three”] > > > > (though there you don’t need an argument to split at all I guess) or > > something like: > > > > irb(main):016:0\> “one!two!three!”.split(“!”) > > =\> [“one”, “two”, “three”] > > Hm, I think that it causes more trouble than it’s worth. I’m not sure what you mean; what trouble does it cause? > It’s very easy to remove empty elements anyway: > > “one!two!three!”.split(“!”).reject { |item| item.empty? } It’s even easier than that 🙂 “one!two!three!”.split(“!”).grep(/\S/) though I’m still not sure what’s undesireable about having split do different things. > Maybe it would be better to create a reject\_at\_end/at\_start or something > similar? That seems like an awfully specific case for a whole separate method. (I admit, though, that I’m somewhat conservative about proliferation of methods 🙂 David > **···** > > On Tue, 1 Jun 2004, Florian Gross wrote: > > – > David A. Black > [dblack@wobblini.net](mailto:dblack@wobblini.net)