Javascript custom sort with special characters dash (-) and underscore (_)

Question

I am trying to do a custom sort like below order

1. special character ( - first, _ last)
2. digit
3. alphabets

For example, if I sort below

var words = ['MBC-PEP-1', 'MBC-PEP01', 'MBC-PEP91', 'MBC-PEPA1', 'MBC-PEPZ1', 'MBC-PEP_1'];

result should be

MBC-PEP-1,MBC-PEP_1,MBC-PEP01,MBC-PEP91,MBC-PEPA1,MBC-PEPZ1

by using my code the result is below

"MBC-PEP-1", "MBC-PEP01", "MBC-PEP91", "MBC-PEP_1", "MBC-PEPA1", "MBC-PEPZ1"

but I need the above sorting order, not sure how to achieve it.

function MySort(alphabet)
{
    return function(a, b) {
        var lowerA = a.toLowerCase()
        var lowerB = b.toLowerCase()
        var index_a = alphabet.indexOf(lowerA[0]),
        index_b = alphabet.indexOf(lowerB[0]);

        if (index_a === index_b) {
            // same first character, sort regular
            if (a < b) {
                return -1;
            } else if (a > b) {
                return 1;
            }
            return 0;
        } else {
            return index_a - index_b;
        }
    }
}

var items = ['MBC-PEP-1', 'MBC-PEP01', 'MBC-PEP91', 'MBC-PEPA1', 'MBC-PEPZ1', 'MBC-PEP_1'],
sorter = MySort('-_0123456789abcdefghijklmnopqrstuvwxyz');

console.log(items.sort(sorter));

Answer 1

I ported an answer from here to JavaScript, which does what you want without using recursion or anything overly complicated:

function MySort(alphabet) {
    return function (a, b) {
       a = a.toLowerCase();
       b = b.toLowerCase();
       var pos1 = 0;
       var pos2 = 0;
       for (var i = 0; i < Math.min(a.length, b.length) && pos1 == pos2; i++) {
          pos1 = alphabet.indexOf(a[i]);
          pos2 = alphabet.indexOf(b[i]);
       }

       if (pos1 == pos2 && a.length != b.length) {
           return o1.length - o2.length;
       }

       return pos1 - pos2;
    };
}
    
var items = ['MBC-PEP-1', 'MBC-PEP01', 'MBC-PEP91', 'MBC-PEPA1', 'MBC-PEPZ1', 'MBC-PEP_1'],
sorter = MySort('-_0123456789abcdefghijklmnopqrstuvwxyz');

console.log(items.sort(sorter));

Answer 2

As Narigo said in their answer, you're only comparing the first character. Here's a different idea that's probably simpler:

function MySort(a, b) {
  a = a.replace("_", ".");
  b = b.replace("_", ".");
  return a.localeCompare(b);
}

var items = ['MBC-PEP-1', 'MBC-PEP01', 'MBC-PEP91', 'MBC-PEPA1', 'MBC-PEPZ1', 'MBC-PEP_1'];

console.log(items.sort(MySort));

We're basically using the normal string comparison, except we change the underscore to a dot to decide the ordering, since it's compatible with what you're trying to achieve.

Answer 3

You are only looking at the first character in your algorithm. You need to check more of your string / the next characters as well. Here is a quick solution using recursion:

function MySort(alphabet)
{
    return function recSorter(a, b) {
        var lowerA = a.toLowerCase()
        var lowerB = b.toLowerCase()
        var index_a = alphabet.indexOf(lowerA[0]),
        index_b = alphabet.indexOf(lowerB[0]);

        if (index_a === index_b && index_a >= 0) {
            return recSorter(a.slice(1), b.slice(1));
        } else {
            return index_a - index_b;
        }
    }
}

var items = ['MBC-PEP-1', 'MBC-PEP01', 'MBC-PEP91', 'MBC-PEPA1', 'MBC-PEPZ1', 'MBC-PEP_1'],
sorter = MySort('-_0123456789abcdefghijklmnopqrstuvwxyz');

console.log(items.sort(sorter));

I'm not sure what you want to happen when you have different lengths of strings, characters outside the alphabet or at other edge cases. For the posted example, this results in the expected order.