Trying to split array into specified amount of subarrays in javascript

Question

I'm writing a function that takes an array and a number parameter and returns the number amount of arrays split from the given array. So the call chunkArrayInGroups(["a", "b", "c", "d"], 2); should return [a,b] [c,d]. My code is returning [a,c] [b,d]. It should be an easy solution, but I still can't figure out.

function chunkArrayInGroups(arr, size) {
// Break it up.

var newarr=[];
var amount=0;
if(arr.length%2===0)
{
  amount=arr.length/size;
}
else
amount=(arr.length/size)+1;
console.log(amount);
for(i=0;i<amount;i++)
{
  newarr[i]=[];
}
console.log(newarr);
for(z=0;z<arr.length;z=z+size)
{

  for(x=0;x<size;x++)
    {
      newarr[x].push(arr[z+x]);

    }


   }
  console.log(newarr);
   }

  chunkArrayInGroups(["a", "b", "c", "d"], 2);

Also, if you see bad syntax please correct me, I'm used to writing Java. Thank you!

Ori Drori · Accepted Answer · 2017-08-02 16:32:20Z

2

Run over all the items in the array, and whenever the index % size is 0, add another sub array, then push the item to the last sub array.

function chunkArrayInGroups(arr, size) {
  var chunks = [];
  
  for(var i = 0; i < arr.length; i++) {    
    if(i % size === 0) {
      chunks.push([]);
    }
    
    chunks[chunks.length - 1].push(arr[i]);
  }
  
  return chunks;
}

console.log('Size 2', JSON.stringify(chunkArrayInGroups(['a', 'b', 'c', 'd'], 2)));
console.log('Size 3', JSON.stringify(chunkArrayInGroups(['a', 'b', 'c', 'd'], 3)));
console.log('Size 4', JSON.stringify(chunkArrayInGroups(['a', 'b', 'c', 'd'], 4)));
console.log('Size 6', JSON.stringify(chunkArrayInGroups(['a', 'b', 'c', 'd'], 6)));

edited Aug 2, 2017 at 16:32

answered Aug 2, 2017 at 16:27

Ori Drori

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Comments

baao · Accepted Answer · 2017-08-02 16:31:16Z

0

You could use the Array.slice method together with the loop to chunk an array:

function chunkArrayInGroups(arr, size) {
  let i,j,res = [];
  for (i=0,j=arr.length; i<j; i+=size) {
    res.push(arr.slice(i,i+size));
  }
  return res;
}

console.log(chunkArrayInGroups(["a", "b", "c", "d"], 2));

answered Aug 2, 2017 at 16:31

baao

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Comments

Seb Morris · Accepted Answer · 2017-08-02 16:32:59Z

0

The issue comes from newarr[x].push(arr[z+x]);.

Each time the second loop runs, it adds 1 letter to the first array inside newarr and 1 letter to the second array inside newarr.

This is because x inside the loop (in the case of size = 2), starts as 0 (the first array) and then becomes 1 (the second array).

To fix this problem: newarr[x].push(arr[z+x]); should be changed to newarr[z/size].push(arr[z+x]);

answered Aug 2, 2017 at 16:32

Seb Morris

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Comments

Redu · Accepted Answer · 2017-08-02 19:05:04Z

0

This would be my solution;

function chunkArrayInGroups(a,n){
  return n > 0 ? n <= a.length ? a.reduce((r,e,i) => (r[Math.floor(n*i/a.length)].push(e),r), Array(n).fill().map(_ => [])) : a : a;
}

var a      = ["a", "b", "c", "d","e"],
    n      = 3;
    result = chunkArrayInGroups(a,n);
console.log(result);

edited Aug 2, 2017 at 19:05

answered Aug 2, 2017 at 18:59

Redu

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Nina Scholz · Accepted Answer · 2017-08-02 21:26:31Z

0

Beside the given answers, you could use another approach with Array#reduce and check if you need a new array for a new chunk.

function chunkArrayInGroups(array, size) {
    return array.reduce(function(r, a, i, aa) {
        i % Math.ceil(aa.length / size) || r.push([]);
        r[r.length - 1].push(a);
        return r;
    }, []);
}

console.log(chunkArrayInGroups(["a", "b", "c", "d", "e"], 3));

edited Aug 2, 2017 at 21:26

answered Aug 2, 2017 at 16:41

Nina Scholz

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1 Comment

Redu Over a year ago

This returns [ [ 'a', 'b', 'c' ], [ 'd' ] ] if the second parameter is 3.

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