Sorting an integer's digits in descending order

Question

So say we have a number -- 123456 for simplicity sake. I needed a function that would take that as input and return 654321, or say 53283940, same would return 98543320.

I have something seems to work I'm just not sure if it's done with best practice, it seems like it can be re-factored into something cleaner. Here is what I have, any help? I'm new trying to improve, thank you.

function descendingOrder(a){
    let b = Array.from(a.toString()).map(Number); // map int into array
    let stringResult = b.sort().reverse().join(""); // sort in ascending, then reverse & join
    let intResult = ~~stringResult; // double bitwise operator to turn str to int
    return intResult; // return final int
}

that is what it takes. You'll be offered some optimizations but they all do the same (but more efficiently). — Randy Casburn, Jun 21 '19 at 21:20
you need no map with `Number`, because you can sort by string, as you do later. — Nina Scholz, Jun 21 '19 at 21:23
Mixing `Number` and `~~` to do the same operation in two different ways could be improved. — Bergi, Jun 21 '19 at 21:38
The biggest problem with javascript numbers is that they are limited in size. So if you try your function on some big one, like `1999999999999`, the result will be surprising. — georg, Jun 21 '19 at 22:01

Ghoul Ahmed · Accepted Answer · 2019-06-21T21:35:25.383

3

Try this:

const sortNumber = (a) => Number([...("" + a)].sort().reverse().join(""));

const test1 = 123456;
console.log(sortNumber(test1));

const test2 = 53283940;
console.log(sortNumber(test2));

or

const sortNumber = (a) => ~~Array.from(a.toString()).sort().reverse().join("");

const test1 = 123456;
console.log(sortNumber(test1));

const test2 = 53283940;
console.log(sortNumber(test2));

edited Jun 21 '19 at 21:35

answered Jun 21 '19 at 21:21

Ghoul Ahmed

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This returns a string, I need it to return a number. Nice solution otherwise! – exception-io Jun 21 '19 at 21:25
2

You can prefix the return value with a '+' to cast to an int: `(a) => +Array.from(a.toString()).sort().reverse().join("")` – Brian Jun 21 '19 at 21:25
Can I prefix it with double bitwise as well? `~~` – exception-io Jun 21 '19 at 21:26
Yes, be wary of truncating floats for general use though – Brian Jun 21 '19 at 21:28
@exception-io, return will be number, cast to Number like this Number( [...("" + a)].sort().reverse().join("")) – Ghoul Ahmed Jun 21 '19 at 21:29

Sorting an integer's digits in descending order

1 Answers1