Explanation

Our goal for this Algorithm is to split arr (first argument) into smaller chunks of arrays with the length provided by size (second argument). There are 4 green checks (objectives) our code needs to pass in order to complete this Algorithm: 1. (['a', 'b', 'c', 'd'], 2) is expected to be [['a', 'b'], ['c', 'd']] 2. ([0, 1, 2, 3, 4, 5], 3) is expected to be [[0, 1, 2], [3, 4, 5]] 3. ([0, 1, 2, 3, 4, 5], 2) is expected to be [[0, 1], [2, 3], [4, 5]] 4. ([0, 1, 2, 3, 4, 5], 4) is expected to be [[0, 1, 2, 3], [4, 5]]

Click More information under the Algorithm title and read the helpful links if you haven't yet.

How to approach the Algorithm

The helpful links suggest to use Array.push() so let's start by first creating a new array to store the smaller arrays we will soon have like this:

var newArray = [];

Next we'll need a for loop to loop through arr then finally we need a method to do the actual splitting and we can use Array.slice() to do that. The key to this Algorithm is understanding how a for loop, size, Array.slice() and Array.push() all work together.

How does a for loop and Array.slice() work

For Loop

A for loop keeps looping until a condition evaluates to false for example if we had:

for (var i = 0; i < arr.length; i++)

i starts with a value of 0, i loops until i is no longer less than the length of arr and during each repeat loop, the value of i increases by 1 (one). If arr.length happens to be 4 then the for loop stops right before i reaches 4.

Array.slice() Method

Array.slice() method extracts a portion of an array and returns a copy into a new array. We can declare which element to start and which element to stop. For example, if arr is ['a', 'b', 'c', 'd'] and we used arr.slice(1, 3);, the Array.slice() method starts at element 1 and stops at element 3 then returns:

["b","c"]

Notice how it captures the start element but doesn't capture the stop element.

Using a for loop and Array.slice() together

If we use the following for loop while size is 2 (note: size = 2):

(var i = 0; i < arr.length; i += size)

The loop starts at element 0, loops once then i += 2 which is another way of stating i = i + 2 so now the new value of i becomes 2. What happens if we combine the following arr.slice() with the for loop?

arr.slice(i, i + size)

Push the arrays out

We can combine the Array.slice() method with the Array.push() method inside the for loop like this:

for (var i = 0; i < arr.length; i += size) {
newArray.push(arr.slice(i, i + size));
}

arr.slice() will start at element 0 and stop at element 2. Here's the fun part: once the for loop, loops again then the value of i becomes 2 while the i in the arr.slice() will also have a value of 2. The new arr.slice() becomes:

arr.slice(2, 2 + 2)

Now arr.slice() starts at the element 2 and stops at element 4 and in the next loop, arr.slice() will start at element 4 and stop at element 6. newArray.push() will push all the elements out into chunks of smaller arrays with the length of size.

Spoiler Alert!

Solution ahead!

Code Solution:

Solution 1:

function chunk(arr, size) {

  var temp = [];
  var result = [];

  for (var a = 0; a < arr.length; a++) {
    if (a % size !== size - 1)
      temp.push(arr[a]);
    else {
      temp.push(arr[a]);
      result.push(temp);
      temp = [];
    }
  }

  if (temp.length !== 0)
    result.push(temp);
  return result;
}

Solution 2:

function chunk(arr, size) {
  // Break it up
  // It's already broken :(
  arr = arr.slice();
  var arr2 = [];
  for(var i = 0, len = arr.length; i < len; i+=size) {
    arr2.push(arr.slice(0, size));
    arr = arr.slice(size);
  }
  return arr2;
}

Solution 3:

function chunk(arr, size) {
  // Break it up.
  var newArr = [];
  var i = 0;

  while (i < arr.length) {
    newArr.push(arr.slice(i, i+size));
    i += size;
  }
  return newArr;
}
chunk(["a", "b", "c", "d"], 2);

Solution 4:

// splice & slice, avoiding size counting
function chunk(arr, size) {
  var ar = arr.slice();
  var res = [];
  do {
    res.push(ar.splice(0, size));
  } while (ar.length > 0);
  return res;
}

Credits:

If you found this page useful, you can give thanks by copying and pasting this on the main chat: Thanks @kirah1314 @Rafase282 @jsommamtek @oshliaer for your help with Algorithm: Chunky Monkey

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