regular expression match if groups same

Question

I'm trying to match iff two capture groups are the same. I could manually check after the match, but I'm wondering if there is a way I can do this in the expression itself.

My expression is (\d+)\/(\d+), so I only want to accept strings where the two numbers are equal. Is there a nice way to check this in the regular expression, or do I have to manually check groups after?

EDIT: This was marked a duplicate but the supposed duplicate question is not related and does not in any way answer my question...

Use `r'\b(\d+)/\1\b'` (or `r'^(\d+)/\1$` if the whole input is in `num/num` format). — Wiktor Stribiżew, Apr 26 '17 at 08:28

Stephane Janicaud · Accepted Answer · 2017-04-26T08:43:21.970

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You can use this one in python : \b(\d+)\/+\1\b

Demo

This is the same usecase as checking for doubled words

When editing text, doubled words such as "the the" easily creep in. Using the regex \b(\w+)\s+\1\b in your text editor, you can easily find them. To delete the second word, simply type in \1 as the replacement text and click the Replace button.

Source

edited Apr 26 '17 at 08:43

answered Apr 26 '17 at 08:31

Stephane Janicaud

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Pedro Lobito · Answer 2 · 2017-04-26T08:43:36.870

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I assume you don't have any other capture groups, based on that:

\b(\d+)\/(\1)\b

Regex Demo

edited Apr 26 '17 at 08:43

answered Apr 26 '17 at 08:34

Pedro Lobito

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Care to comment the downvote? – Pedro Lobito Apr 26 '17 at 08:34
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wasnt my downvote, but i imagine lack of explanation? – chris Apr 26 '17 at 08:38
Same for me, I've added an answer, almost the same as Wiktor, again ;), but with a example on regex101 that took me the 2 more minutes and it was immediatly downvoted without any explication/comment. It's ridiculous, I deleted it. – Stephane Janicaud Apr 26 '17 at 08:38
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Undelete my answer with more information. Maybe it'll help @chris. – Stephane Janicaud Apr 26 '17 at 08:44
@chris https://ideone.com/mktlxJ – Pedro Lobito Apr 26 '17 at 08:50
I don't know if this deserves a new question, but what should one do when trying to match strings that must have the ```(\d+)\/(\d+)``` but when the first number should be different from the second? – olenscki Dec 01 '22 at 22:19

regular expression match if groups same

2 Answers2