order roman-numbers in javascript

Question

I have a function in javascript where the schoolClass it's an roman number like this I, II, IV etc. this function is called multiple times and the result it's concatenated in an array like this:

const generateClasses = (schoolClass, number) => {
  const classes = [];

  for (let i = 0; i < number; i++) {
    classes.push(`${schoolClass}-${(i + 10).toString(36).toUpperCase()}`);
  }
  return classes;
};
let output = [];
output = output.concat(generateClasses('II', 2));
output = output.concat(generateClasses('I', 1));
output = output.concat(generateClasses('IV', 2));
console.log(output);

in the end the output it's like this:

["II-A", "II-B", "I-A", "IV-A", "IV-B"]

how to order the array-like ["I-A", "II-A", "II-B", "IV-A", "IV-V"] I appreciate any help! PS: for converting numbers in roman I use the roman-numbers module

Use sort, split the string on -, convert the roman numeral into a number (plenty of scripts out there), compare it — epascarello, Dec 11 '20 at 13:59
can you show me an example? for converting numbers in roman I use the `roman-numbers` module — Cosmin Ciolacu, Dec 11 '20 at 14:02
@CosminCiolacu, please first try, and if it doesn't work, show your code (that attempts to order the data) in the question and indicate where you are stuck with it. — trincot, Dec 11 '20 at 14:03
What is the greatest Roman number you will ever get in your input? — trincot, Dec 11 '20 at 14:18
@trincot for school grades, I expect XII. Although I'm not sure if all countries have 12 school grades. — VLAZ, Dec 11 '20 at 14:20

VLAZ · Accepted Answer · 2020-12-11T14:16:06.087

You need to convert the Roman numeral to a normal (Arabic) one to compare. Since you have very constrained amount of Roman numerals, the easiest way is to just hardcode them - no need to involve an algorithm that transforms them if you only have 12 different possible inputs.

With hardcoded values for I to XII, you can sort based on multiple criteria by splitting your string on - and:

sort by the part before the dash as a number.
the part after the dash as a string.

const romanTable = {
  "I"   : 1,
  "II"  : 2,
  "III" : 3,
  "IV"  : 4,
  "V"   : 5,
  "VI"  : 6,
  "VII" : 7,
  "VIII": 8,
  "IX"  : 9,
  "X"   : 10,
  "XI"  : 11,
  "XII" : 12,
};

const arr = ["II-A", "II-B", "I-A", "IV-A", "IV-B"];

arr.sort((a, b) => {
  const [mainA, secondaryA] = a.split("-");
  const [mainB, secondaryB] = b.split("-");
  
  if (mainA !== mainB)
    return romanTable[mainA] - romanTable[mainB];
   
  return secondaryA.localeCompare(secondaryB);
});

console.log(arr);

score 2 · Answer 2 · answered Dec 11 '20 at 14:30

2

As school grades are limited to 12, the alphabetical sort isn't that bad to start with. For the example you have given you could just call .sort() on that array and it would be fine.

Actually, only "IX" would get sorted at the wrong place. So let's deal with that:

let classes = ["XII-A", "IX-A", "VII-A", "II-A", "II-B", "I-A", "IV-A", "IV-B"];
let trans = s => s.replace("IX", "VIIJ");
classes.sort((a, b) => trans(a).localeCompare(trans(b)));
console.log(classes);

This would work for Roman numbers that don't use any other symbols than I, V and X, so up to 39.

answered Dec 11 '20 at 14:30

trincot

317,000
35
244
286

Quite clever. I'd probably change `s.replace("IX", "VIIII")` - it's kind of technically correct. At least more intuitive than adding a J. – VLAZ Dec 11 '20 at 14:33
1

Looking at your nick, I should probably have chosen "VIIZ" ;-) – trincot Dec 11 '20 at 14:34
1

:D makes it sounds like a number invented during the ancient Roman zombie apocalypse. – VLAZ Dec 11 '20 at 14:36

score 0 · Answer 3 · answered Dec 11 '20 at 14:16

Here I converted the Roman to Integer by iterating each Roman character So XII will be (10+1+1)

Now Sort them but if 2 Roman character are same than I compare the Alphabet attached with it.

const num = ["II-B", "II-A", "I-A", "IV-A", "IV-B"];

num.sort((a, b) => {
  const diff = roman_to_Int(a.split("-")[0]) - roman_to_Int(b.split('-')[0]);
  if (diff === 0) {
    return a.split("-")[1].localeCompare(b.split("-")[1]);
  }
  return diff;

});

console.log(num);

/* Source - https://www.w3resource.com/javascript-exercises/javascript-math-exercise-22.php */

function roman_to_Int(str1) {
  if(str1 == null) return -1;
  var num = char_to_int(str1.charAt(0));
  var pre, curr;
  for(var i = 1; i < str1.length; i++){
    curr = char_to_int(str1.charAt(i));
    pre = char_to_int(str1.charAt(i-1));
    if(curr <= pre){
      num += curr;
    } else {
      num = num - pre*2 + curr;
    }
  }
  return num;
}

function char_to_int(c){
    switch (c){
      case 'I': return 1;
      case 'V': return 5;
      case 'X': return 10;
      case 'L': return 50;
      case 'C': return 100;
      case 'D': return 500;
      case 'M': return 1000;
      default: return -1;
    }
}

order roman-numbers in javascript

3 Answers3