Question

176

Use of capture groups in String.split()

rated 0 times [ 178] [ 2] / answers: 1 / hits: 13530 / 11 Years ago, wed, january 29, 2014, 12:00:00

$ node

> ababaabab.split(/a{2}/)

[ 'abab', 'bab' ]

> ababaabab.split(/(a){2}/)

[ 'abab', 'a', 'bab' ]

>

So, this doesn't make sense to me. Can someone explain it? I don't get why the 'a' shows up.

Note: I am trying to match for doubled line endings (possibly on windows files) so I am splitting on /(r?n){2}/. However I get extraneous '15n' entries in my array (note 15 == r).

Why are these showing up?

Note: also affects JS engine in browsers so this is specific to JS not node.

Answers

Only authorized users can answer the question. Please sign in first, or register a free account.

trinityr

Add To Favorites

Follow

Total Points: 49

Total Questions: 107

Total Answers: 96

Location: Mayotte

Member since Fri, Oct 1, 2021

3 Years ago

trinityr questions

1 Parsing Error : Identifier 'App' has already been declared

Mon, Feb 28, 22, 00:00, 2 Years ago

1 Failed to resolve module specifier firebase/app

Fri, Sep 17, 21, 00:00, 3 Years ago

1 React has detected a change in the order of Hooks called by Navigation

Wed, Sep 8, 21, 00:00, 3 Years ago

1 ValidationError: Invalid configuration object. Webpack has been initialized using a configuration object that does not match the API schema. Next.js

Fri, Jun 18, 21, 00:00, 3 Years ago

1 useHistory not defined in react custom Hook

Wed, Feb 17, 21, 00:00, 3 Years ago

View All

answered 11 Years ago alenaautump · Accepted Answer

In your second result, a is appearing because you've wrapped it in a capture group () (parentheses).

If you want to not include it but you still require a conditional group, use a non-capturing group: (?:a). The questionmark-colon can be used inside any capture group and it will be omitted from the resulting list of captures.

Here's a simple example of this in action: http://regex101.com/r/yM1vM4