Regex - Match repeated character not in sequence

Question

Is there a way to match repeated characters that are not in a sequence?

Let's say I'm looking for at least two 6s in the string.

var string = "61236";

I can only find quantifiers that match either zero or one or characters in a sequence.

River

Can they be in sequence as well? – Languishment

Yes. But does not have to. – River

Answer 1

Here is a regexp that matches a character that is followed somehwere in the string by the same digit:

/(.)(?=.*?\1)/

Usage:

var test = '0612364';
test.match(/(.)(?=.*?\1)/)[0] // 6

DEMO: https://regex101.com/r/xU1rG4/4

Here is one that matches it repeated at least 3 times (total of 4+ occurances)

/(.)(?=(.*?\1){3,})/

DEMO: https://regex101.com/r/xU1rG4/3

Kitkitchen

Maybe add a lazy qualifier so that the .* doesn't match all the way to the right before looking for a backreference match: /(\d)(?=.*?\1)/ – Croce

@MikeSamuel Added, thanks. I can't seem to add a maximum amount of occurances to the regex. Does anyone have any ideas? I tried [^\1] instead of ., but that is the character 1, tried {3,5}, but that just matches the \d with .. – Kitkitchen

to match a maximum, you need to ensure that the .*? does not match \1: (?:(?!=\1).)*? – Croce

Awesome! It works. Thank you! Damn you guys are fast. – River

@MikeSamuel I tried that in the meantime, but it doesn't seem to work: regex101.com/r/iL2dQ1 Perhaps i made a stupid mistake? – Kitkitchen

You should update your regex101 link. It does not show exactly the queries you are trying here now. I tried to fix it until I realized the earlier version was also incorrect. – Mediative

@Mediative The original link was for the generic regex101 sample, so when you edited it and created a new version, the original link pointed towards your version. I fixed it and added another version for the last example. – Kitkitchen

I didnt change the link at all or save a new version. The first DEMO still does not match the code you have show here (which I was trying to fix but became hesitant). It does match an earlier version of this answer though. – Mediative

Answer 2

Have a try with this regex:

/(.).*?\1/

Mandatory

Answer 3

Match 6 and anything up until another 6

!!"61236".match("6.*6")
// returns true

Match 6 and anything up until another the same as the first group (which is a 6)

!!"61236".match(/(6).*\1/)
// returns true

Annabelleannabergite

What are those !! doing in the beginning? Is that js? – River

@KarlPokus it converts the value returned by match to a boolean. If a match is found, the resulting array gets converted to true, otherwise null gets converted to false. – Kitkitchen

Answer 4

Characters that are not in sequence and appear more than once:

/(.)(.+\1)+/

Mosasaur

Answer 5

You can remove the ? after .* since the .* already matches zero or more characters.

(.)(?=.*\1)

var test = "0612364";
console.log(
  test.match(/(.)(?=.*\1)/)[0]
);

Underfoot