CODEWITHSUNDEEP
javascriptregex
mark0matic
mark0matic

Reputation: 73

How to find and replace every nth character occurrence using regex?

How can I find and replace for example every third occurrence of 'x' character in string with regular expression?

There is similar question but it addresses every fourth character but I need every "nth" occurrence of specific character in string.

I'm using JavaScript replace() method, this below example will change every x character to y:

replace(/\x/g, 'y')

But how can I write regex for question above?

Some random text for example, and expected result:

I amx nexver axt hoxme on Sxundxaxs.

to:

I amx nexver ayt hoxme on Sxundyaxs.

I can use JS for loop with split() and join() but solution with replace() method seams more elegant.

Upvotes: 7

Views: 13363

Answers (1)

anubhava
anubhava

Reputation: 784998

You can use:

str = str.replace(/((?:[^x]*x){2}[^x]*)x/g, '$1y');

So if you are searching for every 3rd occurrence then use n-1 between {} in above regex.

To build it dynamically use:

let str = 'I amx nexver axt hoxme on Sxundxaxs';
let n = 3;
let ch = 'x';

let regex = new RegExp("((?:[^" +ch+ "]*" +ch+ "){" + (n-1) + "}[^" +ch+ "]*)" +ch, "g");

str = str.replace(regex, '$1y');

console.log(str);
//=> I amx nexver ayt hoxme on Sxundyaxs

RegEx Demo

Upvotes: 14

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