如何使用正则表达式查找以三个字符开头的单词 [英] How to use regular expressions to find words that begin with a three character prefix

问题描述

我的目标是计算以一个以上字母的指定前缀开头的单词(字符串中)的数量.一种情况是以"non"开头的单词.所以在这个例子中...

My goal is to count the number of words (in a string) that begin with a specified prefix of more than one letter. A case is words that begin with "non". So in this example...

NSString * theFullTestString = @"nonsense non-issue anonymous controlWord";

...我想在废话"和非问题"上获得成功，但在匿名"或"controlWord"上却没有获得成功.我的总点击数应为2.

...I want to get hits on "nonsense" and "non-issue", but not on "anonymous" or "controlWord". The total count of my hits should be 2.

所以这是我的测试代码，看起来似乎很接近，但是我尝试过的所有正则表达式都无法正常工作.此代码捕获废话"(正确)和匿名"(错误)，但不捕获非问题"(错误).它的计数为2，但原因不正确.

So here's my test code which seems close, but none of the regular expression forms I've tried works correctly. This code catches "nonsense" (correct) and "anonymous" (wrong) but not "non-issue" (wrong). Its count is 2, but for the wrong reason.

NSUInteger countOfNons = 0;
NSString * theFullTestString = @"nonsense non-issue anonymous controlWord";
NSError *error = nil;

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"non(\\w+)" options:0 error:&error];

NSArray *matches = [regex matchesInString:theFullTestString options:0 range:NSMakeRange(0, theFullTestString.length)];

for (NSTextCheckingResult *match in matches) {
    NSRange wordRange = [match rangeAtIndex:1];
    NSString* word = [theFullTestString substringWithRange:wordRange];
    ++countOfNons;
    NSLog(@"Found word:%@  countOfNons:%d", word, countOfNons);
}

我很困惑.

推荐答案

正则表达式 \ bnon [\ w-] * 应该可以解决问题

The regex \bnon[\w-]* should do the trick

\bnon[\w-]*
^ (\b) Start of word
  ^ (non) Begins with non
     ^ ([\w-]) A alphanumeric char, or hyphen
          ^ (*) The character after 'non' zero or more times

因此，在您的情况下:

NSUInteger countOfNons = 0;
NSString * theFullTestString = @"nonsense non-issue anonymous controlWord";
NSError *error = nil;

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:@"(\\bnon[\\w-]*)" options:0 error:&error];

NSArray *matches = [regex matchesInString:theFullTestString options:0 range:NSMakeRange(0, theFullTestString.length)];

for (NSTextCheckingResult *match in matches) {
    NSRange wordRange = [match rangeAtIndex:1];
    NSString* word = [theFullTestString substringWithRange:wordRange];
    ++countOfNons;
    NSLog(@"Found word:%@  countOfNons:%d", word, countOfNons);
}

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