+1 for string.count i don’t think the g-flag is necessary in str.split, so the original performance claims are still valid: - for counting regexp - use split + length - for counting substring - use while + indexOf
> On 20 Jan 2019, at 12:22 AM, Isiah Meadows <isiahmead...@gmail.com> wrote: > > Nit: you should use `.spilt(/\n/g)` to get all parts. > > I like the benchmarks here. That's much appreciated, and after further > investigation, I found a *giant* WTF: > https://jsperf.com/regexp-counting-2/8 > > TL;DR: for string character counting, prefer `indexOf`. > > For similar reasons to that JSPerf thing, I'd like it to be on the > String prototype rather than the RegExp prototype, as in > `str.count(/\n/)`. > > ----- > > Isiah Meadows > cont...@isiahmeadows.com > www.isiahmeadows.com > > On Sun, Jan 20, 2019 at 12:33 AM kai zhu <kaizhu...@gmail.com> wrote: >> >> benchmarked @isiah’s while-loop test-case vs str.split vs str.replace for >> regexp counting on jsperf.com [1], and the results were surprising (for me). >> >> benchmarks using 1mb random ascii-string from fastest to slowest. >> 1. (fastest - 1,700 runs/sec) regexp-counting with >> ```largeCode.split(/\n/).length - 1``` >> 2. (40% slower - 1000 runs/sec) regexp-counting with ```while-loop (/n/g)``` >> 3. (60% slower - 700 runs/sec) regexp-counting with >> ```largeCode.replace((/[^\n]+/g), "").length``` >> >> looks like the go-to design-pattern for counting-regexp is >> ```str.split(<regexp>).length - 1``` >> >> [1] regexp counting 2 >> https://jsperf.com/regexp-counting-2 >> >> On 13 Jan 2019, at 9:15 PM, Isiah Meadows <isiahmead...@gmail.com> wrote: >> >> If performance is an issue, regular expressions are likely to be too slow to >> begin with. But you could always do this to count the number of lines in a >> particular string: >> >> ```js >> var count = 0 >> var re = /\n|\r\n?/g >> while (re.test(str)) count++ >> console.log(count) >> ``` >> >> Given it's already this easy to iterate something with a regexp, I'm not >> convinced it's necessary to add this property/method. >> On Sat, Jan 12, 2019 at 17:29 kai zhu <kaizhu...@gmail.com> wrote: >>> >>> a common use-case i have is counting newlines in largish (> 200kb) >>> embedded-js files, like this real-world example [1]. ultimately meant for >>> line-number-preservation purposes in auto-lint/auto-prettify tasks (which >>> have been getting slower due to complexity). >>> >>> would a new RegExp count-method like ```(/\n/g).count(largeCode)``` be >>> significantly more efficient than existing ```largeCode.split("\n").length >>> - 1``` or ```largeCode.replace((/[^\n]+/g), "").length```? >>> >>> -kai >>> >>> [1] calculating and reproducing line-number offsets when linting/autofixing >>> files >>> https://github.com/kaizhu256/node-utility2/blob/2018.12.30/lib.jslint.js#L7377 >>> https://github.com/kaizhu256/node-utility2/blob/2018.12.30/lib.jslint.js#L7586 >>> >>> _______________________________________________ >>> es-discuss mailing list >>> es-discuss@mozilla.org >>> https://mail.mozilla.org/listinfo/es-discuss >> >> _______________________________________________ es-discuss mailing list es-discuss@mozilla.org https://mail.mozilla.org/listinfo/es-discuss
