javascript - 每个起始字母只匹配一个单词

Question

你可以在这里看到我希望如何过滤单词:

string = 'Take all first words for each letter... this is a test';
first_letters = {};

words = string.match(/\w+/g);
words.forEach(function(x){
    var first = x[0].toLowerCase();
    first_letters[first] = (first_letters[first] || x);
});

result = [];
for (var x in first_letters) {
    result.push(first_letters[x]);
}

O.innerHTML = result;

<pre id=O>

我正在尝试仅使用正则表达式获取上面显示的数组 result，我开始尝试首先获取首字母:

result = words.match(/\b(?!\1)(\w)/gi);

但是 (?!\1) 并没有像我想象的那样过滤字母。可以看到here .

欢迎任何帮助。谢谢

Answer 1

此正则表达式将仅查找唯一的首字母:

r = /\b(\w)(?!.*\b\1)/gi;

这个正则表达式说:

Find the first letter after a word break, but only if that same letter does not occur immediately after a word break later in the string (negative lookahead).

string = 'Take all first words for each letter... this is a test';

> string.match(r)
< ["w", "f", "e", "l", "i", "a", "t"]

为每个唯一的第一个字母找到一个词:

r = /\b((\w)\w*)(?!.*\b\2)/gi

> string.match(r)
< ["words", "for", "each", "letter", "is", "a", "test"]

正如@karthik manchala 在评论中提到的，由于正则表达式的限制，这只会找到以每个字母开头的last 单词。要找到以每个字母开头的第一个 单词，您必须反转字符串中的单词:

> string . split(' ') . reverse() . join(' ') . match(r) . reverse()
< ["Take", "all", "first", "words", "each", "letter", "is"]

你的初始正则表达式

/\b(?!\1)(\w)/gi

无法正常运行，因为 \1 必须引用较早的捕获组。