# String#split: unxepected result

**URL:** <https://www.ruby-forum.com/t/string-split-unxepected-result/74572>\
**Category:** Ruby\
**Created:** [November 7, 2006, 10:48am UTC](https://www.ruby-forum.com/t/string-split-unxepected-result/74572 "2006-11-07T10:48:36Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![sheynkman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/5f9b8f/32.png) [@sheynkman](https://www.ruby-forum.com/u/sheynkman)\
**Post date:** [November 7, 2006, 10:48am UTC](https://www.ruby-forum.com/t/string-split-unxepected-result/74572/1 "2006-11-07T10:48:36Z")

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irb(main):001:0\> “aabbcc”.split(/bb/)  
=\> [“aa”, “cc”]  
irb(main):002:0\> “aabbcc”.split(/(bb)/)  
=\> [“aa”, “bb”, “cc”]  
irb(main):003:0\> “aabbcc”.split(/bb©?/)  
=\> [“aa”, “c”, “c”]

The last two result is unexpected for me. Can anybody explain it?

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**Author:** ![sheynkman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/5f9b8f/32.png) [@sheynkman](https://www.ruby-forum.com/u/sheynkman)\
**Post date:** [November 7, 2006, 10:48am UTC](https://www.ruby-forum.com/t/string-split-unxepected-result/74572/2 "2006-11-07T10:48:37Z")

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On 31.10.2006 10:49, Kirill S. wrote:

> irb(main):001:0\> “aabbcc”.split(/bb/)  
> =\> [“aa”, “cc”]  
> irb(main):002:0\> “aabbcc”.split(/(bb)/)  
> =\> [“aa”, “bb”, “cc”]  
> irb(main):003:0\> “aabbcc”.split(/bb©?/)  
> =\> [“aa”, “c”, “c”]
> 
> The last two result is unexpected for me. Can anybody explain it?

#split returns matching groups of the split pattern if there are  
capturing groups:

irb(main):008:0\> “aabbcc”.split(/bb©?/)  
=\> [“aa”, “c”, “c”]  
irb(main):009:0\> “aabbcc”.split(/bb(?:c)?/)  
=\> [“aa”, “c”]  
irb(main):010:0\> “aabbcc”.split(/(bb(?:c)?)/)  
=\> [“aa”, “bbc”, “c”]

Regards

```
robert
```

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<div class="post-metadata">

**Author:** ![sheynkman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/5f9b8f/32.png) [@sheynkman](https://www.ruby-forum.com/u/sheynkman)\
**Post date:** [November 7, 2006, 10:48am UTC](https://www.ruby-forum.com/t/string-split-unxepected-result/74572/3 "2006-11-07T10:48:37Z")

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Kirill S. wrote:

> irb(main):001:0\> “aabbcc”.split(/bb/)  
> =\> [“aa”, “cc”]  
> irb(main):002:0\> “aabbcc”.split(/(bb)/)  
> =\> [“aa”, “bb”, “cc”]  
> irb(main):003:0\> “aabbcc”.split(/bb©?/)  
> =\> [“aa”, “c”, “c”]
> 
> The last two result is unexpected for me. Can anybody explain it?

You have a capturing group in the last RE. In this case, split also  
returns capturing groups. See for instance

> > str = “abcd”  
> > =\> “abcd”
> 
> > p str.split(/(b)/)  
> > [“a”, “b”, “cd”]

The string is split into “a” and “cd”, and in the middle you get the  
result of the capturing group, “b”. You want a non-capturing group,  
(?:c) instead of ©

Cheers !

```
Vince
```

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**Author:** ![sheynkman](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/5f9b8f/32.png) [@sheynkman](https://www.ruby-forum.com/u/sheynkman)\
**Post date:** [November 7, 2006, 10:48am UTC](https://www.ruby-forum.com/t/string-split-unxepected-result/74572/4 "2006-11-07T10:48:38Z")

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On 10/31/06, Kirill S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> irb(main):001:0\> “aabbcc”.split(/bb/)  
> =\> [“aa”, “cc”]  
> irb(main):002:0\> “aabbcc”.split(/(bb)/)  
> =\> [“aa”, “bb”, “cc”]  
> irb(main):003:0\> “aabbcc”.split(/bb(c)?/)  
> =\> [“aa”, “c”, “c”]
> 
> The last two result is unexpected for me. Can anybody explain it?

If there are any groups in the delimiter, they are output as well.  
This is not documented in RDoc, only in the PickAxe book.

It’s useful when you want to keep the delimiters.