Regex remove repeated characters from a string by javascript

Question

I have found a way to remove repeated characters from a string using regular expressions.

function RemoveDuplicates() {
    var str = "aaabbbccc";
    var filtered = str.replace(/[^\w\s]|(.)\1/gi, "");  
    alert(filtered);
}

Output: abc this is working fine.

But if str = "aaabbbccccabbbbcccccc" then output is abcabc. Is there any way to get only unique characters or remove all duplicates one? Please let me know if there is any way.

Does the order matter? In other words, is it necessary that the first occurrence of the character is the one you save? — Firas Dib
– Firas Dib, Commented Oct 10, 2013 at 17:01
i want characters in same sequence after remove duplicates one. Only unique one. — SK.
– SK., Commented Oct 10, 2013 at 17:04

Mosh Feu · Accepted Answer · 2018-10-08 17:03:35Z

59

A lookahead like "this, followed by something and this":

var str = "aaabbbccccabbbbcccccc";
console.log(str.replace(/(.)(?=.*\1)/g, "")); // "abc"

Note that this preserves the last occurrence of each character:

var str = "aabbccxccbbaa";
console.log(str.replace(/(.)(?=.*\1)/g, "")); // "xcba"

Without regexes, preserving order:

var str = "aabbccxccbbaa";
console.log(str.split("").filter(function(x, n, s) {
  return s.indexOf(x) == n
}).join("")); // "abcx"

edited Oct 8, 2018 at 17:03

Mosh Feu

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answered Oct 10, 2013 at 17:00

georg

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4 Comments

Firas Dib Over a year ago

I asked Mike but he has not answered yet. Your solution is the one I would have gone with, and if you need to preserve order, wouldn't str.split("").reverse().join("") do the trick?

SK. Over a year ago

by running this code... string is not coming in same seqeunce. if var str = "aaabbbcccaabbbcccaaaaaaaasa"; output = "bcsa" but i want something like abcs

georg Over a year ago

@Lindrian: yes, that, or some other method from blog.stevenlevithan.com/archives/mimic-lookbehind-javascript

Daniel Duong Over a year ago

How would you preserve the first occurance?

Ivan Sivak · Accepted Answer · 2017-07-26 09:52:26Z

14

This is an old question, but in ES6 we can use Sets. The code looks like this:

var test = 'aaabbbcccaabbbcccaaaaaaaasa';
var result = Array.from(new Set(test)).join('');

console.log(result);

answered Jul 26, 2017 at 9:52

Ivan Sivak

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Comments

Ignas · Accepted Answer · 2025-03-19 09:33:01Z

0

All examples above ignore letter if it appears again later. For example string 'aaabbbcccaaa' will become just 'abc' not 'abca'. For this (preserve each multiple occurence) I used this function:

function removeSameLetters(str){
    return str.replace(/(.)\1+/g, '$1');
}
console.log(removeSameLetters('aaabbbcccaa'));

answered Mar 19 at 9:33

Ignas

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