Reduce JSON array to object with combined key-values

Question

I have an array like this:

[
    { "avl_res": 1, "res_status": "Available", "code": "AAA" },
    { "avl_res": 2, "res_status": "Unavailable", "code": "AAA" },
    { "avl_res": 2, "res_status": "Available", "code": "BBB" },
    { "avl_res": 1, "res_status": "Available", "code": "CCC" },
    { "avl_res": 5, "res_status": "Unavailable", "code": "CCC" },
    { "avl_res": 3, "res_status": "Unavailable", "code": "DDD" },
];

I am trying to produce this:

[
    {"avl_res":1,"total_res":3,"code":"AAA"},
    {"avl_res":2,"total_res":2,"code":"BBB"},
    {"avl_res":1,"total_res":6,"code":"CCC"},
    {"avl_res":0,"total_res":3,"code":"DDD"},
];

Following the answer to this question, I managed to do it with this:

var singles = {};
arr.forEach(function (item) {
    var single = singles[item.code] = singles[item.code] || {};
    single[item.res_status] = item.avl_res;
});

var outputList = [];
for (var single in singles) {
    let total_res = 0;
    let avl_res = 0;

    singles[single]['Available'] ? avl_res = singles[single]['Available'] : avl_res = 0;
    singles[single]['Unavailable'] ? total_res = avl_res + singles[single]['Unavailable'] : total_res = avl_res;

    outputList.push({ code: single, total_res: total_res, avl_res: avl_res });
}

console.log(outputList);

Just wondering if this is efficient enough or there's a better/elegant way, maybe by using other JS functions (e.g. reduce, map, etc.). Cheers!

I’m voting to close this question because this questions belongs on Code Review. — adiga
– adiga, Commented Apr 26, 2021 at 5:44
Noted @adiga. I'll post this kind of question in the proper section next time. Thanks! — Konstabel Piksel
– Konstabel Piksel, Commented May 6, 2021 at 7:48

Nur · Accepted Answer · 2021-04-26 08:48:29Z

1

If you care code performance (efficiency) that much, You would like this...

const arr = [
    { "avl_res": 1, "res_status": "Available", "code": "AAA" },
    { "avl_res": 2, "res_status": "Unavailable", "code": "AAA" },
    { "avl_res": 2, "res_status": "Available", "code": "BBB" },
    { "avl_res": 1, "res_status": "Available", "code": "CCC" },
    { "avl_res": 5, "res_status": "Unavailable", "code": "CCC" },
    { "avl_res": 3, "res_status": "Unavailable", "code": "DDD" },
];

const results = [];
const findItem = {};

for (const { avl_res, code, res_status } of arr) {
    let item = findItem[code];
    const res = res_status == 'Available' ? avl_res : 0;
    if (item) {
        item.total_res += avl_res;
        item.avl_res += res;
    }
    else {
        item = { avl_res: res, total_res: avl_res, code };
        results.push(item);
        findItem[code] = item;
    }
}
console.log(results);

edited Apr 26, 2021 at 8:48

answered Apr 26, 2021 at 6:29

Nur

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4 Comments

adiga Over a year ago

Why not use a plain find object instead of adding that as a property to array?

Nur Over a year ago

There is no problem to use find() But In this case, I just want to write super efficiency code, Even we should trust efficiency about build in function in JavaScript, Although find() is not just loop, it use function as loop, and function call is expensive...

adiga Over a year ago

I didn't mean array.find method. I meant why not use a const find = {} object directly instead of adding that property to the array like results.find . Arrays shouldn't be assigned anything other than an integer property

Nur Over a year ago

Although in my case, Its fine to do, But for your (@adiga) sake, I edited my answer...

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