Increment for first element in multi dimensional array

Question

I have an array that looks like: [x, y]. While y will always remain constant. I want x to be incremented by 100 every iteration.

This is what I did:

let arr = [
    {
        "name": "pies",
        "data": [
            [
                "us",
                149045
            ],
            [
                "es",
                41746
            ],
            [
                "uk",
                37640
            ],
            [
                "au",
                16594
            ]
        ],
    },
    {
        "name": "cakes",
        "data": [
            [
                "us",
                128845
            ],
            [
                "es",
                35752
            ],
            [
                "uk",
                32246
            ],
            [
                "au",
                14333
            ]
        ],
    }
];

let inc = 100;
arr.forEach(d=> {
    d['m_arr'] = [inc, 125];
    inc +100;
});

console.log(arr);

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

As you can see, it is not incrementing the value. It is always just inserting [100, 125]. In the first object with the name, pies I want the m_arr: [100, 125] and the next object with the name, cakes to be [200, 125].

How do I do that?

typo? inc +100 => inc += 100

KooiInc
– KooiInc

2021-04-01 15:05:00 +00:00
Commented Apr 1, 2021 at 15:05 — KooiInc
– KooiInc, Commented Apr 1, 2021 at 15:05
Why not use .map instead of .forEach?

evolutionxbox
– evolutionxbox

2021-04-01 15:05:54 +00:00
Commented Apr 1, 2021 at 15:05 — evolutionxbox
– evolutionxbox, Commented Apr 1, 2021 at 15:05
@KooiInc that was it! Thanks for noticing!

nb_nb_nb
– nb_nb_nb

2021-04-01 15:06:32 +00:00
Commented Apr 1, 2021 at 15:06 — nb_nb_nb
– nb_nb_nb, Commented Apr 1, 2021 at 15:06
I dont see any x or y here

Kai Lehmann
– Kai Lehmann

2021-04-01 15:07:30 +00:00
Commented Apr 1, 2021 at 15:07 — Kai Lehmann
– Kai Lehmann, Commented Apr 1, 2021 at 15:07
@KaiLehmann, I used x and y as an example for array format

nb_nb_nb
– nb_nb_nb

2021-04-01 15:07:58 +00:00
Commented Apr 1, 2021 at 15:07 — nb_nb_nb
– nb_nb_nb, Commented Apr 1, 2021 at 15:07

callumery 11 · Accepted Answer · 2021-04-01 15:11:12Z

1

The problem is that your varible that stores the value the original 100 (inc) its new value is never set. This line inc + 100 will take the value of inc add 100 then forget it because its not stored. what you should be doing is using += to update the existing value.

answered Apr 1, 2021 at 15:11

callumery 11

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Comments

Brandon McConnell · Accepted Answer · 2021-04-01 15:39:21Z

I believe this is a simplified version of what you are trying to achieve here. Rather than setting up an inc variable which you may later need to reset if you plan to re-use the function, just use the iterator parameter included in the forEach method (2nd param). By adding 1 to this value and then multiplying by 100, you should always have the desired value. Here it is in action:

let arr = [
    {
        name: "pies",
        data: [
            ["us", 149045],
            ["es", 41746],
            ["uk", 37640],
            ["au", 16594]
        ],
    }, {
        name: "cakes",
        data: [
            ["us", 128845],
            ["es", 35752],
            ["uk", 32246],
            ["au", 14333]
        ],
    }
];

arr.forEach((d,i) => d.m_arr = [(i+1)*100, 125]);

console.log(arr); // returns the below ↓↓↓

[
    {
        name: "pies",
        data: [
            ["us", 149045],
            ["es", 41746],
            ["uk", 37640],
            ["au", 16594]
        ],
        m_arr: [100, 125]
    }, {
        name: "cakes",
        data: [
            ["us", 128845],
            ["es", 35752],
            ["uk", 32246],
            ["au", 14333]
        ],
        m_arr: [200, 125]
    }
];

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