Question

I’m looking for a RegEx to return either the first [n] words in a paragraph or, if the paragraph contains less than [n] words, the complete paragraph is returned.

For example, assuming I need, at most, the first 7 words:

<p>one two <tag>three</tag> four five, six seven eight nine ten.</p><p>ignore</p>

I’d get:

one two <tag>three</tag> four five, six seven

And the same RegEx on a paragraph containing less than the requested number of words:

<p>one two <tag>three</tag> four five.</p><p>ignore</p>

Would simply return:

one two <tag>three</tag> four five.

My attempt at the problem resulted in the following RegEx:

^(?:\<p.*?\>)((?:\w+\b.*?){1,7}).*(?:\</p\>)

However, this returns just the first word – “one”. It doesn’t work. I think the .*? (after the \w+\b) is causing problems.

Where am I going wrong? Can anyone present a RegEx that will work?

FYI, I’m using .Net 3.5’s RegEX engine (via C#)

Many thanks

Answer 1

OK, complete re-edit to acknowledge the new “spec” 🙂

I’m pretty sure you can’t do that with one regex. The best tool definitely is an HTML parser. The closest I can get with regexes is a two-step approach.

First, isolate each paragraph’s contents with:

<p>(.*?)</p>

You need to set RegexOptions.Singleline if paragraphs can span multiple lines.

Then, in a next step, iterate over your matches and apply the following regex once on each match’s Group[1].Value:

((?:(\S+\s+){1,6})\w+)

That will match the first seven items separated by spaces/tabs/newlines, ignoring any trailing punctuation or non-word characters.

BUT it will treat a tag separated by spaces as one of those items, i. e. in

One, two three <br\> four five six seven

it will only match up until six. I guess that regex-wise, there’s no way around that.