Showing unique characters in a string only once

Question

I have a string with repeated letters. I want letters that are repeated more than once to show only once. For instance I have a string aaabbbccc i want the result to be abc. so far my function works like this:

• if the letter doesn't repeat, it's not shown
• if it's repeated once, it's show only once (i.e. aa shows a)
• if it's repeated twice, shows all (i.e. aaa shows aaa)
• if it's repeated 3 times, it shows 6 (if aaaa it shows aaaaaa)

function unique_char(string) {
    var unique = '';
    var count = 0;
    for (var i = 0; i < string.length; i++) {
        for (var j = i+1; j < string.length; j++) {
            if (string[i] == string[j]) {
                count++;
                unique += string[i];
            }
        }
    }
    return unique;
}

document.write(unique_char('aaabbbccc'));

The function must be with loop inside a loop; that's why the second for is inside the first.

Answer 1

Fill a Set with the characters and concatenate its unique entries:

function makeUnique(str) {
  return String.prototype.concat(...new Set(str))
}

console.log(makeUnique('abc'));    // "abc"
console.log(makeUnique('abcabc')); // "abc"

Answer 2

Convert it to an array first, then use the answer here, and rejoin, like so:

var nonUnique = "ababdefegg";
var unique = nonUnique.split('').filter(function(item, i, ar){ return ar.indexOf(item) === i; }).join('');

All in one line :-)

Answer 3

Using lodash:

_.uniq('aaabbbccc').join(''); // gives 'abc'

Answer 4

Too late may be but still my version of answer to this post:

function extractUniqCharacters(str){
    var temp = {};
    for(var oindex=0;oindex<str.length;oindex++){
        temp[str.charAt(oindex)] = 0; //Assign any value
    }
    return Object.keys(temp).join("");
}