How can I sort a JavaScript array by specific criteria?

Question

I have an array like:

[0,0,1,1,0,0,2,2,2,0...]

I have to pass for each element a letter in this form:

[A, B, C1, C2, D, E, F1, F2, F3, G...]

When the value is zero, or undefined or null need a new letter, otherwise need a new one again but as times as the same number stays there. There are two of 1 then I need C1, C2, later is there three of 2 so I need F three times.

Can you give me some hints to solve this issue?

Also, what happens if you have [0, 0, 1, 1, 2, 2]? Do you start a new letter sequence for the 2s or continue the old one? — VLAZ
– VLAZ, Commented Jun 29, 2021 at 14:54
What is the expected output? A flat array like this: [C1, C2, F1, F1, F2, F2, ...]? — adiga
– adiga, Commented Jun 29, 2021 at 14:56

Nina Scholz · Accepted Answer · 2021-06-30 20:50:16Z

2

You could take a closure over letter and count and return eiter the same letter as before with count or just the letter.

const
    values = [0, 0, 1, 1, 2, 2, 3, 3, 3, 0],
    result = values.map(((letter, count) => (v, i, { [i - 1]: prev }) => {
        if (v) {
            if (prev && v !== prev) {
                ++letter;
                count = 1;
            }
            return letter.toString(36).toUpperCase() + count++;
        }
        if (count !== 1) ++letter;
        count = 1;
        return (letter++).toString(36).toUpperCase();
    })(10, 1));

console.log(...result);

edited Jun 30, 2021 at 20:50

answered Jun 29, 2021 at 14:57

Nina Scholz

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5 Comments

Dániel Boros Over a year ago

I have stuck with your script a bit in that case when I have an array like for example [0, 0, 1, 1, 2, 2, 3, 3, 3, 0]. I get results [A, B, C1, C2, C3, C4, C5, C6, C7, D] so at 1 and 2 and 2 and 3 don't change the letter.

Nina Scholz Over a year ago

@DánielBoros, it needs another check. please see edit.

Dániel Boros Over a year ago

it seems good, but the number should start from 1 when the letters are changed. Sorry I was not exact.

Dániel Boros Over a year ago

I think I should take count = 1 in the second if statement and everything will be perfect.

Dániel Boros Over a year ago

I need for result an array like this: [A B C1 C2 D1 D2 E1 E2 E3 F]

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