Javascript array calculation and transformation

Question

I currently struggle to program a receipt calculator. I want to map over an array with a specific value, then round the numbers and convert they to a string with commas instead of dots.

let ingredients = [0.02, 0.05, 0.5, 1.2];

let map = ingredients.map(x => x * 6);

for (let entry of map)
{
    entry.toFixed(2).replace(".", ",");
    console.log(entry);
}

This is what I get using a quantity of 6 on the mapping procedure:

0.12; 0.30000000000000004; 3; 7.199999999999999

But instead, I want it to be like:

0,12; 0,3; 3; 7,2

On a side note, it's written ingredients, not ingridients. — Nino Filiu
– Nino Filiu, Commented Feb 13, 2019 at 19:39

Maheer Ali · Accepted Answer · 2019-02-13 19:46:59Z

4

entry.toFixed(2).replace(".", ",") doesn't change the entry it return a new value.You need to assign entry a new value.

let quantity = 4;

let ingridients = [ 0.02, 0.05, 0.5, 1.2 ];
let map = ingridients.map(x => x * quantity);

for (let entry of map) {
  entry = entry.toFixed(2).replace(".", ",");
  console.log(entry);
}

edited Feb 13, 2019 at 19:46

answered Feb 13, 2019 at 19:36

Maheer Ali

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Comments

Ben West · Accepted Answer · 2019-02-13 19:35:52Z

3

entry.toFixed(2).replace(".", ","); doesn't change entry. You need to assign it to something.

let formatted = entry.toFixed(2).replace(".", ",")
console.log( formatted )

answered Feb 13, 2019 at 19:35

Ben West

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Comments

Jonas Wilms · Accepted Answer · 2019-02-13 19:37:29Z

2

Both .toFixed and replace are pure (as any other method working with primitives) that means they do not change the referenced value itself but return a new value. If you'd do

console.log(entry.toFixed(2).replace(".", ","));

you would log the wanted returned value.

answered Feb 13, 2019 at 19:37

Jonas Wilms

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Comments

Shidersz · Accepted Answer · 2019-09-15 21:26:17Z

1

One solution to the precision problem you are facing when performing arithmetic operations with float numbers could be approached using a correction factor. A correction factor will be that number you need to multiply to the float number so that it gets converted into an integer. In this sense, all the arithmetic operations will now perform between integers numbers. You can check the next code to see how to use a correction factor in this particular case:

let quantity = 6;
let ingredients = [0.02, 0.05, 0.5, 1.2];

// Define a correction factor for arithmetic operations within
// the set of float numbers available on ingredients.
let cf = Math.pow(10, 2);

let map = ingredients.map(x =>
{
    let res = (x * cf) * (quantity * cf) / (cf * cf);
    return res.toString().replace(".", ",");
});

let mapRounded = ingredients.map(x =>
{
    let res = (x * cf) * (quantity * cf) / (cf * cf);
    return Math.ceil(res);
});

console.log("Original: ", map, "Rounded-Up: ", mapRounded);

.as-console {background-color:black !important; color:lime;}
.as-console-wrapper {max-height:100% !important; top:0;}

edited Sep 15, 2019 at 21:26

answered Feb 13, 2019 at 20:54

Shidersz

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2 Comments

flowyyy Over a year ago

Thanks. This was the must useful answer to my problem. Im now trying to implement that if map[2] has a comma (eg. 3,5) it should always round up to the next integer... like 4. Can you help me with that?

Shidersz Over a year ago

@aura199x you can create another map of rounded-up elements, with Math.ceil(). I have updated my answer, check if this helps you.

zero298 · Accepted Answer · 2019-02-13 19:36:30Z

0

let ingridients = [ 0.02, 0.05, 0.5, 1.2 ];
let quantity = 6;

let map = ingridients
    .map(x => x * quantity)
    .map(n => n.toFixed(2).replace(".", ","));

for (let entry of map) {
  console.log(entry);
}

answered Feb 13, 2019 at 19:36

zero298

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1 Comment

flowyyy Over a year ago

Is this the more elegant way? Or the answer from @Maheer Ali ? Thanks

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