Array Multiplication in Javascript

Question

I am trying to multiply child array elements. Can you please have a look below code and let me know if we can do more optimization.

Note:- I want to push the multiplied value of child arrays in another array.

Can you please help me with this.

var arr1 = [
    [3, 2],
    [2, 3],
    [4, 5]
]

var sumArr = [];
for (var row = 0; row < arr1.length; row++) {
    var fullRow = arr1[row];
    var val = 1;
    for (var col = 0; col < fullRow.length; col++) {
        val *= fullRow[col];
    }
    sumArr.push(val);

}
console.log(sumArr);

What do you mean by "optimization"?

Aadit M Shah
– Aadit M Shah

2018-12-18 19:19:05 +00:00
Commented Dec 18, 2018 at 19:19 — Aadit M Shah
– Aadit M Shah, Commented Dec 18, 2018 at 19:19
This is related to javascript

Ian Lim
– Ian Lim

2018-12-19 00:43:30 +00:00
Commented Dec 19, 2018 at 0:43 — Ian Lim
– Ian Lim, Commented Dec 19, 2018 at 0:43
What is the expected output? Does this code work?

iagowp
– iagowp

2018-12-19 00:45:17 +00:00
Commented Dec 19, 2018 at 0:45 — iagowp
– iagowp, Commented Dec 19, 2018 at 0:45

Aadit M Shah · Accepted Answer · 2018-12-18 19:24:29Z

1

The best way to do this would be to use map and reduce as follows:

const arr1 = [ [3, 2]
             , [2, 3]
             , [4, 5]
             ];

const multiply = (a, b) => a * b;

const product = arr => arr.reduce(multiply, 1);

const sumArr = arr1.map(product);

console.log(sumArr);

I'm not sure what you mean by "optimization" but is this what you're looking for?

answered Dec 18, 2018 at 19:24

Aadit M Shah

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5 Comments

Adrian Brand Over a year ago

This doesn't deal well with an edge case of [] as it will return 1 instead of 0

Aadit M Shah Over a year ago

It's supposed to return 1 because that is the identity element of multiplication. It's not supposed to return 0 because that is the absorbing element of multiplication.

Adrian Brand Over a year ago

The multiplication of no elements is 1?

Adrian Brand Over a year ago

If you asked me what is the product of nothing I would answer nothing.

Aadit M Shah Over a year ago

For multiplication 1 is "nothing". The "nothing" that you are referring to is the identity element. This makes sense because when you convert numbers into their logarithms then multiplication becomes addition and 1 becomes 0. However, 0 becomes undefined.

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