Dividing array into sub-arrays based on number of groups

Question

This is kind of confusing so I will just demonstrate. I would like to create a function that takes an array like this:

[1, 2, 3, 4, 5, 6, 7]

...and returns an array of arrays like this:

[[1, 5], [2, 6], [3, 7], [4]]

assuming that the user wanted 4 groups. Notice that the elements are added to each group before 5th element is added back to the first.

Is there a simple way to do this? My project is using webpack, so I am open to ES6+ or even lodash. Thanks!

Please also explain what you are trying to do, what happens if the array has an even number of elements? — Luca Kiebel
– Luca Kiebel, Commented May 28, 2018 at 20:22
And what's the pattern? I mean, why it's 1 with 5 and not 1 with 6? — Mitca Vicentiu
– Mitca Vicentiu, Commented May 28, 2018 at 20:23
@Luca Well, I am rearranging an array of DOM elements but I thought the number examples was simpler. If perhaps there were 10 elements and 4 groups, it would look like [[1, 5, 9], [2, 6, 10], [3, 7], [4, 8]] — Eric Phillips
– Eric Phillips, Commented May 28, 2018 at 20:24
@MitcaVicentiu There are 4 groups, and so 1 through 4 go in the first groups, and then 5 starts back at the very first, six to the second, and so on. — Eric Phillips
– Eric Phillips, Commented May 28, 2018 at 20:26

gaetanoM · Accepted Answer · 2018-05-28 20:40:29Z

3

My proposal is:

var numGroups= 4;
var result = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].reduce(function(acc, ele, idx) {
    var i = idx % numGroups;
    (acc[i] == undefined) ?  acc[i] = [ele] : acc[i].push(ele);
    return acc;
}, []);

console.log(result);

answered May 28, 2018 at 20:40

gaetanoM

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1 Comment

Eric Phillips Over a year ago

Perfect! Thank you so much! If you wouldn't mind, could you just give a very brief explanation?

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