英文:
JavaScript: Match a regex and return only part of the result?
问题
这会返回 150 calorie，但我想要的只是 150。可以尝试以下方法来仅使用正则表达式实现：
const t = "The 2 items contained 150 calories";
const match = t.match(/(\d+) calorie/);
const result = match ? match[1] : null;
// 现在，result 包含了所需的值，如果匹配成功的话
这段代码会返回匹配的数字部分 150，如果匹配失败，则 result 为 null。
英文:
I know this is possible but I can't find the answer with the Google keywords I'm using, so I'm asking this in the hope it helps someone else too.
I'd like to regex match a substring but only return part of that substring.
Here's my attempt:
const t = "The 2 items contained 150 calories";
t.match(/(\d+) calorie/g).replace(" calorie", "");
This returns 150 calorie but what I want is just 150.
I can hack it with t.match(/(\d+) calorie/g)[0].replace(" calorie", "") but perhaps there's a way to do it just with regexes?
答案1
得分: 1
你可以使用正则表达式前瞻：
const t = "The 2 items contained 150 calories";
const result = t.match(/(\d+)(?= calorie)/g);
console.log(result);
如果您需要进一步解释或有其他问题，请告诉我。
英文:
You can use regex lookaheads:
<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-js -->
const t = "The 2 items contained 150 calories";
const result = t.match(/(\d+)(?= calorie)/g)
console.log(result);
<!-- end snippet -->
答案2
得分: 1
你几乎正确，尽管你不能在.match后使用.replace，因为后者返回一个类似数组的对象。移除g标志，并使用[1]获取第一个捕获组：
const t = "The 2 items contained 150 calories";
const num = t.match(/(\d+) calorie/)[1];
console.log(num);
顺便说一下，如果你担心字符串不匹配你的正则表达式，可以使用这个方式：
const t = "The 2 items contained 150 calories";
const m = t.match(/(\d+) calorie/);
const num = m ? m[1] : null;
console.log(num);
你也可以像@Live bug help解释的那样使用正向预查，但请注意，这不是在所有浏览器中都通用，特别是Safari。
英文:
You were close, although you can't use a .replace after a .match because the latter returns an array like object. Remove the g flag, and get the first capture group with [1]:
<!-- begin snippet: js hide: false console: true babel: false -->
<!-- language: lang-js -->
const t = "The 2 items contained 150 calories";
const num = t.match(/(\d+) calorie/)[1];
console.log(num);
<!-- end snippet -->
BTW, if you are concerned about a string not matching your regex use this instead:
const t = "The 2 items contained 150 calories";
const m = t.match(/(\d+) calorie/);
const num = m ? m[1] : null;
console.log(num);
You can also use a positive lookahead as @Live bug help explained, but please note that that is not universally supported, notably Safari.
答案3
得分: 0
我不懂JavaScript，但我认为正则表达式与Python中的相同。在我的示例中，'t'是您的文本字符串。
解释：
- \d+ 匹配1个或更多数字（或\ d匹配单个数字）
- (?:/\d+)? 可选地匹配/和1个或更多数字
- (?= 正向前瞻，用于断言右侧紧接着的内容是
- \s?calories?\b 匹配可选的空白字符，然后是calories或calories
- ) 关闭前瞻
代码：
result = re.findall(r"\d+(?:/\d+)?(?=\s?calories?\b)", t)
print(result) # 只会打印150
英文:
I don’t know JavaScript, but I think regex is equal as in python. In my example ‘t’ is your text string.
Explanation:
<li>\d+ Match 1+ digits (Or \d for a single digit) </li>
<li>(?:/\d+)? Optionally match / and 1+ digits </li>
<li>(?= Positive lookahead to assert what is directly at the right is </li>
<li>\s?calories?\b Match an optional whitspace char followed by calories or calories </li>
<li>) Close the lookahead
</li>
code:
<pre>
result = re.findall(r"\d+(?:/\d+)?(?=\s?calories?\b)", t)
print(result) # will print 150 only
</pre>
Source: Stack Overflow
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