How to find the sum of the elements of an arbitrary JavaScript array

Question

There is such an arbitrary array in which I need to find the sum of all numbers without using Array.isArray:

let arr = [[1, 2, 3, [4, 5, [6, 7]]], [8, [9, 10]]];

The solution should look something like this:

let arr = [[1, 2, 3, 4, 5], [6, 7, 8], [9, 10]]; 

for (let i = 0; i < arr.length; i++) { 
   for (let j = 0; j < arr[i].length; j++) { 
      console.log(arr[i][j]);
   }
}

Could you please advise me on how to achieve this?

can you flatten the array and simply use for loop to calculate the sum ? — Mohammad Basit
– Mohammad Basit, Commented Sep 12, 2020 at 8:27
This requires some form of recursion or stack that can handle “N” nesting levels, at some level - the solution concept shown will fail on the input within 3 levels of nesting. It will also need some method to determine if an element is an array (or is not a number), even if it’s not “isArray”. — user2864740
– user2864740, Commented Sep 12, 2020 at 8:37

pygeek · Accepted Answer · 2020-09-12 08:43:38Z

1

Solution

Use flat and reduce methods to accomplish this.

Example

let arr = [[1, 2, 
3, [4, 5, [6, 7]]], 
[8, [9, 10]]];

arr.flat(Infinity).reduce((a, b) => a + b, 0)

References

Flat: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat

Reduce: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce

edited Sep 12, 2020 at 8:43

answered Sep 12, 2020 at 8:37

pygeek

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1 Comment

Mohammad Basit Over a year ago

This is giving a wrong output. I think you need to pass Infinity as an argument to flat()

Nina Scholz · Accepted Answer · 2020-09-12 08:37:31Z

You could take Array#flat and Array#reduce the array or check the instance of the given value with instanceof operator.

function getSum1(array) {
    return array.flat(Infinity).reduce((sum, value) => sum + value, 0);
}

function getSum2(array) {
    let sum = 0;
    for (const value of array) {
        sum += value instanceof Array
            ? getSum2(value)
            : value
    }
    return sum;
}

let array = [[1, 2, 3, [4, 5, [6, 7]]], [8, [9, 10]]];

console.log(getSum1(array));
console.log(getSum2(array));

Ravi · Accepted Answer · 2020-09-12 08:42:54Z

-1

you use lodash for this:

var _ = require("lodash");
var arr = [[1, 2, 3, [4, 5, [6, 7]]], [8, [9, 10]]];
flatArr = _.flattenDeep(arr);
flatArr.reduce((sum, value) => sum + value, 0);

answered Sep 12, 2020 at 8:42

Ravi

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3 Comments

Ravi Over a year ago

what was the issue for giving -1?

pygeek Over a year ago

Possibly because the additional dependency is unnecessary.

Ravi Over a year ago

I have provided an alternative solution. Which was not mentioned above

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