Slice an array to multiple parts

Question

My example:

let arr = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18];

let slice = (source, index) => source.slice(index, index + 4);

let length = arr.length;

let index = 0;

let result = [];

while (index < length) {
  let temp = slice(arr, index);
  
  result.push(temp);
  
  index += 4;
}

console.log(result);

Logging:

[[1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16],[17,18]]

I want to slice the array to multiple parts for per 4 items [1,2,3,4] [5,6,7,8]...

The code is working fine.

I have 2 questions:

1/. Is there another way to do that via using inline code? Ex: result = arr.slice(...)

2/. After I define:

let push = result.push;

why cannot I still use:

push(temp)

Error message:

Uncaught TypeError: Array.prototype.push called on null or undefined

UPDATE: I've updated the solution based on the answers. Hope it's helpful.

let arr = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18];

let result = [];

arr.forEach((x,y,z) => !(y % 4) ? result.push(z.slice(y, y + 4)) : '');

console.log(result);

Logging:

[[1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16],[17,18]]

`let push = result.push;` extracts the function so that it's no longer associated with any certain object. You would need to use `push.call(result, temp)` — 4castle, Feb 21 '17 at 15:54

beta-developper · Accepted Answer · 2017-02-21T16:06:36.020

3

A simple way to do it

var chunckArray = function(array, chunkCount){
     var chunks = [];
     while(array.length){
         chunks.push(array.splice(0, chunkCount);
     }
     return chunks;
}

A non consumative way :

var chunckArray = function(array, chunkCount){
     var chunks = [],  i, j;
     for (i = 0, j = array.length; i<j; i+= chunkCount) {
         chunks.push(array.slice(i, i + chunkCount); 
     }
     return chunks;
}

edited Feb 21 '17 at 16:06

answered Feb 21 '17 at 16:01

beta-developper

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It would be worth shallow cloning it to keep the desired behaviour and not mutate the original – Balázs Édes Feb 21 '17 at 16:04
You are right buddy – beta-developper Feb 21 '17 at 16:04

score 2 · Answer 2 · answered Feb 21 '17 at 16:11

You can also do it using a for loop which will give you a same result:

let arr = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18];

console.log(arr.length);
var result=[];

for(var i = 0; i < arr.length; i+=4) {
  result=arr.slice(i, i+4);
  console.log(result);
}

score 1 · Answer 3 · answered Feb 21 '17 at 16:04

I've done this using a simple reduce (see plnkr):

let arr = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18];

var counter = -1;
var result = arr.reduce((final, curr, i) => {
  if (i % 4 === 0) {
    final.push([curr])
    counter++;
  } else {
    final[counter].push(curr);
  }

  return final;
}, []);

console.log(result);

You can tweak the 4 and substitute it with a variable chuckSize this will allow you to be able reapply to other things - you could also wrap this in a function with paramerters (array, chunkSize) if you wanted to

Slice an array to multiple parts

3 Answers3