d 效率低于 [0-9] [英] d less efficient than [0-9]

问题描述

我昨天对某人在正则表​​达式中使用了 [0123456789] 而不是 [0-9] 或 d 的答案发表了评论代码>.我说过使用范围或数字说明符可能比使用字符集更有效.

I made a comment yesterday on an answer where someone had used [0123456789] in a regex rather than [0-9] or d. I said it was probably more efficient to use a range or digit specifier than a character set.

我今天决定对此进行测试，结果令我惊讶的是(至少在 c# 正则表达式引擎中)d 似乎比其他两个没有的效率低好像差别很大.这是我的测试输出超过 10000 个随机字符串的 1000 个随机字符，其中 5077 个实际上包含一个数字:

I decided to test that out today and found out to my surprise that (in the c# regex engine at least) d appears to be less efficient than either of the other two which don't seem to differ much. Here is my test output over 10000 random strings of 1000 random characters with 5077 actually containing a digit:

Regex d           took 00:00:00.2141226 result: 5077/10000
Regex [0-9]        took 00:00:00.1357972 result: 5077/10000  63.42 % of first
Regex [0123456789] took 00:00:00.1388997 result: 5077/10000  64.87 % of first

这让我感到惊讶有两个原因，如果有人能解释一下，我会很感兴趣:

It's a surprise to me for two reasons, that I would be interested if anyone can shed some light on:

1. 我原以为范围会比集合更有效地实现.
2. 我不明白为什么 d 比 [0-9] 更糟糕.除了 [0-9] 的简写之外，d 是否还有更多内容?

1. I would have thought the range would be implemented much more efficiently than the set.
2. I can't understand why d is worse than [0-9]. Is there more to d than simply shorthand for [0-9]?

测试代码如下:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Text.RegularExpressions;

namespace SO_RegexPerformance
{
    class Program
    {
        static void Main(string[] args)
        {
            var rand = new Random(1234);
            var strings = new List<string>();
            //10K random strings
            for (var i = 0; i < 10000; i++)
            {
                //generate random string
                var sb = new StringBuilder();
                for (var c = 0; c < 1000; c++)
                {
                    //add a-z randomly
                    sb.Append((char)('a' + rand.Next(26)));
                }
                //in roughly 50% of them, put a digit
                if (rand.Next(2) == 0)
                {
                    //replace 1 char with a digit 0-9
                    sb[rand.Next(sb.Length)] = (char)('0' + rand.Next(10));
                }
                strings.Add(sb.ToString());
            }

            var baseTime = testPerfomance(strings, @"d");
            Console.WriteLine();
            var testTime = testPerfomance(strings, "[0-9]");
            Console.WriteLine("  {0:P2} of first", testTime.TotalMilliseconds / baseTime.TotalMilliseconds);
            testTime = testPerfomance(strings, "[0123456789]");
            Console.WriteLine("  {0:P2} of first", testTime.TotalMilliseconds / baseTime.TotalMilliseconds);
        }

        private static TimeSpan testPerfomance(List<string> strings, string regex)
        {
            var sw = new Stopwatch();

            int successes = 0;

            var rex = new Regex(regex);

            sw.Start();
            foreach (var str in strings)
            {
                if (rex.Match(str).Success)
                {
                    successes++;
                }
            }
            sw.Stop();

            Console.Write("Regex {0,-12} took {1} result: {2}/{3}", regex, sw.Elapsed, successes, strings.Count);

            return sw.Elapsed;
        }
    }
}

推荐答案

d 检查所有 Unicode 数字，而 [0-9] 仅限于这 10 个字符.例如，波斯数字，۱۲۳۴۵۶۷۸۹，是Unicode数字的一个例子与 d 匹配，但不与 [0-9] 匹配.

d checks all Unicode digits, while [0-9] is limited to these 10 characters. For example, Persian digits, ۱۲۳۴۵۶۷۸۹, are an example of Unicode digits which are matched with d, but not [0-9].

您可以使用以下代码生成所有此类字符的列表:

You can generate a list of all such characters using the following code:

var sb = new StringBuilder();
for(UInt16 i = 0; i < UInt16.MaxValue; i++)
{
    string str = Convert.ToChar(i).ToString();
    if (Regex.IsMatch(str, @"d"))
        sb.Append(str);
}
Console.WriteLine(sb.ToString());

产生:

012345678901234567890123456789߀߁߂߃߄߅߆߇߈߉012345678901২345678901234567890123456789୦୧୨୩୪୫୬୭୮୯0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789᠐᠑᠒᠓᠔᠕᠖᠗᠘᠙᥆᥇᥈᥉᥊᥋᥌᥍᥎᥏᧐᧑᧒᧓᧔᧕᧖᧗᧘᧙᭐᭑᭒᭓᭔᭕᭖᭗᭘᭙᮰᮱᮲᮳᮴᮵᮶᮷᮸᮹᱀᱁᱂᱃᱄᱅᱆᱇᱈᱉᱐᱑᱒᱓᱔᱕᱖᱗᱘᱙꘠꘡꘢꘣꘤꘥꘦꘧꘨꘩꣐꣑꣒꣓꣔꣕꣖꣗꣘꣙꤀꤁꤂꤃꤄꤅꤆꤇꤈꤉꩐꩑꩒꩓꩔꩕꩖꩗꩘꩙0123456789

0123456789٠١٢٣٤٥٦٧٨٩۰۱۲۳۴۵۶۷۸۹߀߁߂߃߄߅߆߇߈߉०१२३४५६७८९০১২৩৪৫৬৭৮৯੦੧੨੩੪੫੬੭੮੯૦૧૨૩૪૫૬૭૮૯୦୧୨୩୪୫୬୭୮୯௦௧௨௩௪௫௬௭௮௯౦౧౨౩౪౫౬౭౮౯೦೧೨೩೪೫೬೭೮೯൦൧൨൩൪൫൬൭൮൯๐๑๒๓๔๕๖๗๘๙໐໑໒໓໔໕໖໗໘໙༠༡༢༣༤༥༦༧༨༩၀၁၂၃၄၅၆၇၈၉႐႑႒႓႔႕႖႗႘႙០១២៣៤៥៦៧៨៩᠐᠑᠒᠓᠔᠕᠖᠗᠘᠙᥆᥇᥈᥉᥊᥋᥌᥍᥎᥏᧐᧑᧒᧓᧔᧕᧖᧗᧘᧙᭐᭑᭒᭓᭔᭕᭖᭗᭘᭙᮰᮱᮲᮳᮴᮵᮶᮷᮸᮹᱀᱁᱂᱃᱄᱅᱆᱇᱈᱉᱐᱑᱒᱓᱔᱕᱖᱗᱘᱙꘠꘡꘢꘣꘤꘥꘦꘧꘨꘩꣐꣑꣒꣓꣔꣕꣖꣗꣘꣙꤀꤁꤂꤃꤄꤅꤆꤇꤈꤉꩐꩑꩒꩓꩔꩕꩖꩗꩘꩙０１２３４５６７８９

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