Lodash - How to sum the length of array of array

Question

I have an array of array

const myArrays = [
    [ 1, 2, 3, 4], // length = 4
    [ 1, 2], // length = 2
    [ 1, 2, 3], // length = 3
];

How I get the sum length of all children array?

const length = 4 + 2 + 3

Jacob Phan · Accepted Answer · 2017-08-24 06:34:31Z

4

You can use _.sumBy

const myArrays = [
    [ 1, 2, 3, 4], // length = 4
    [ 1, 2], // length = 2
    [ 1, 2, 3], // length = 3
];

 var length = _.sumBy(myArrays, 'length');
console.log("length =", length);

<script src='https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.js'><</script>

edited Aug 24, 2017 at 6:34

answered Aug 24, 2017 at 5:51

Jacob Phan

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1 Comment

Gruff Bunny Over a year ago

The function passed to sumBy can be replaced with the property iteratee:sumBy(myArrays, 'length').

Hassan Imam · Accepted Answer · 2017-08-24 04:33:32Z

3

You can use _.forEach or _.reduce

const myArrays = [
    [ 1, 2, 3, 4], // length = 4
    [ 1, 2], // length = 2
    [ 1, 2, 3], // length = 3
];

var length = 0;

_.forEach(myArrays, (arr) => length += arr.length);

console.log('Sum of length of inner array using forEach : ', length);

length = _.reduce(myArrays, (len, arr) => { 
  len += arr.length;
  return len;
}, 0);

console.log('Sum of length of inner array using reduce : ', length);

<script src='https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.js'><</script>

edited Aug 24, 2017 at 4:33

answered Aug 24, 2017 at 4:27

Hassan Imam

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