2

I have two arrays. They look like this: 

array price = 14.60, 39.00

and 

array quantity = 10, 5

(quantity is the quantity of items the user want to buy - 10 items from productA and 5 of productB)

Now I want loop through the variables to multiply the price with the quantity.

Like : 

14,60 * 10

and

39,00 * 5

and add the two results to the endPrice variable.

I get the quantity array like this: 

$('.quantity').change(function () {
    quantitys = $('input[type=number]').map(function () {
        return $(this).val();
    }).get();
});

and the different prices like this: 

var prices = $('.priceCell').map(function () {
    return parseFloat($(this).html().trim());
}).get();

And that's what I tried: 

var endPrice = 0;
for (var q = 0; q < quantitys.length; q++) {
    for (var p = 0; p < prices.length; p++) {
    endPrice = quantitys[q] * prices[p];
    }
}

alert(endPrice);

Well, that haven't worked for me so well. Can someone help me there? Doesn't matter if the solution is pure JavaScript or jQuery.

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3
  • Have you checked if quantitys and prices are as you expect them to be? Commented Feb 7, 2017 at 13:54
  • Yeah I did and they exactly like in the question Commented Feb 7, 2017 at 14:00
  • I can only assume that you're getting syntax errors with your variable assignments (Uncaught SyntaxError: Unexpected identifier) since neither of those assignments declare, or initialise, an Array. To do so they should look like: price = [14.60, 39.00]; Note the surrounding square brackets. Commented Feb 7, 2017 at 14:00

6 Answers 6

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3

You are using two loops while you should only use one. Also, add to endPrice by using +=:

var endPrice = 0;
for (var q = 0; q < quantitys.length; q++) {
    endPrice += parseFloat(quantitys[q]) * parseFloat(prices[q]);
}

alert(endPrice);
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Comments

2

1st problem

You were using nested loops thus every quantity would be multiplied by every prices. You only need one loop.

2nd problem

You were using endPrice = .... This will override the endPrice every time you go through this line. You need to use += that will add to the current enbPrice 

var prices = [14.60, 39.00];
var quantities = [10,5];
var endPrice = 0;

for(let i=0, l=prices.length;i<l;i++){
  endPrice += prices[i] * quantities[i];  
}

console.log(endPrice);

EDIT

OP need to have separated totals. (See @David Thomas's answer)

You can use Array.prototype.map() 

var prices = [14.60, 39.00];
var quantities = [10, 5];

var totals = prices.map((p, index) => p * quantities[index]);

console.log(totals);

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5 Comments

Nice ! This works! Is there a way to add the two different results to another way? Like : anotherarray = [ (result of 14.60 * 10), (result of 36.00*5) ]. This would help me alot. I'm still new to JS :)
@WellNo: absolutely, that's exactly what my answer does.
I copy and paste that little snippit for seperated values but this haven't worked for me. I don't really understand what (p, index) is..
@WellNo Check the link to the documentation. This is a callback with p as the current value and index as the index. -- What do you mean by not working ?
Forget what I was said. Works fine now hehe.
2

You can't use the double loop for this. This multiplies every price with every quantity. What you want to do is this:

var endPrice = 0;
for (var i = 0; i < quantitys.length; i++) {
    endPrice += quantitys[i] * prices[i];
}
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Comments

2

To multiply every price in one Array by the number held at the same index in a second Array I'd recommend:

var price = [14.60, 39.00],
    quantity = [10, 5],

    // here we iterate over the price Array, using
    // Array.prototype.map() in order to return a
    // new Array:
    totals = price.map(

        // p: the current array-element of
        //    the Array of prices,
        // index: the index of the current
        // array-element of the Array.

        // using an Arrow function to
        // multiply the price ('p') by
        // the value held in the quantity
        // Array at the same index:
        (p,index) => p * quantity[index]
    );

// logging the created 'totals' Array to the console:
console.log(totals); // [146,195]

// logging the created Array, after joining its
// elements together to form a String with values
// separated with a ',' character:
console.log(totals.join(',')); // "146,195"
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2 Comments

I copy and paste your code and tried it out but I get multiple problems with it. My console is also empty.. no error message at all. var totals = prices.map((p, index) => p * quantitys[index]);
Forget what I said, works perfect now! Thanks alot! :)
1

Close, you're missing += instead of =

endPrice += quantitys[q] * prices[p];

Dependent on your values, you may also want to parse them, so:

endPrice += (parseInt(quantitys[q]) * prices[p]) // you're already parsing prices;

Edit with more information in comments:

Because of the way your code is, they prices are on the same row as the quantities, so they'll be the same. So, the new code will be...

for (var q = 0; q < quantitys.length; q++) {
    endPrice += parseInt(quantitys[q]) * prices[q];
}
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1 Comment

I also tried it with += but this gave me a weird value back ( 808.5 ). And the right result would be around 350 :/
1 

const prices = [14.60, 39.00];
const qty = [10, 5];

const endPrice = prices.reduce((total, price, i) => total + price * qty[i], 0);

console.log(endPrice);

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1 Comment

Beat me to it!!

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