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:
(['a', 'b', 'c', 'd'], 2) is expected to be [['a', 'b'], ['c', 'd']]
([0, 1, 2, 3, 4, 5], 3) is expected to be [[0, 1, 2], [3, 4, 5]]
([0, 1, 2, 3, 4, 5], 2) is expected to be [[0, 1], [2, 3], [4, 5]]
([0, 1, 2, 3, 4, 5], 4) is expected to be [[0, 1, 2, 3], [4, 5]]
The links above suggest to use Array.push(), so letâs start by first creating a new array to store the smaller arrays we will soon have like this:
var newArray = [];
Hint 2
Next weâll need a for loop to loop through arr.
Hint 3
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.
Solutions
Solution 1 (Click to Show/Hide)
function chunkArrayInGroups(arr, size) {
let temp = [];
let result = [];
for (let 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;
}
Code Explanation
Firstly, we create two empty arrays called temp and result, which we will eventually return.
Our for loop loops until a is equal to or more than the length of the array in our test.
Inside our loop, we push to temp using temp.push(arr[a]); if the remainder of a / size is not equal to size - 1.
Otherwise, we push to temp, push temp to the result variable and reset temp to an empty array.
Next, if temp isnât an empty array, we push it to result.
function chunkArrayInGroups(arr, size) {
// Break it up.
let newArr = [];
for (let i = 0; i < arr.length; i += size) {
newArr.push(arr.slice(i, i + size));
}
return newArr;
}
Code Explanation
First, we create an empty array arr2 where we will store our âchunksâ.
The for loop starts at zero, increments by size each time through the loop, and stops when it reaches arr.length.
Note that this for loop does not loop through arr. Instead, we are using the loop to generate numbers we can use as indices to slice the array in the right locations.
Inside our loop, we create each chunk using arr.slice(i, i+size), and add this value to arr2 with arr2.push().
function chunkArrayInGroups(arr, size) {
// Break it up.
let newArr = [];
let i = 0;
while (i < arr.length) {
newArr.push(arr.slice(i, i + size));
i += size;
}
return newArr;
}
chunkArrayInGroups(["a", "b", "c", "d"], 2);
Code Explanation
Firstly, we create two variables. newArr is an empty array which we will push to. We also have the i variable set to zero, for use in our while loop.
Our while loop loops until i is equal to or more than the length of the array in our test.
Inside our loop, we push to the newArr array using arr.slice(i, i+size). For the first time it loops, it will look something like:
newArr.push(arr.slice(1, 1+2))
After we push to newArr, we add the variable of size onto i.
Why is the while loop the advanced solution? I had the intermediate one and to me itâs easier to read. Is it because while loops are faster? If so, is the difference significant?
@Naqin I donât understand it either, I came up with this:
function chunkArrayInGroups(arr, size) {
var newArr = [];
var index = 0;
while (index < arr.length){
newArr.push(arr.slice(index,index+size));
index += size;
}
return newArr;
}
Which I suppose is the advanced one, but afterwards I thought that I could have optimized it further for readability, if I did, I would have ended with the for intermediate solution, but in the end I didnât as it doesnât seem to be much of a difference âŚ
So Iâm also wondering which one is faster in this situation, for or while.
@Naqin I donât think it has to do with the while loop. I think it may have something to do with the fact that the solution is using the .splice() method, which alters the original array. Unless you know exactly what you are doing it is kind of risky to alter the array while you are using it.
function chunkArrayInGroups(arr, size) {
var result = [];
for (var i=0; i<arr.length/size; i++){
result.push(arr.slice(size*i, size*(i+1)));
}
return result;
}
The first time you see function newChunks, Iâm declaring the function. Inside the function newChunks I then call it inside itself so it automatically repeats (the recursion). Basically you are saying do function newChunks and then do it again indefinitely. This is why you need a condition in the function so it doesnât go on forever.
Then finally at the bottom, I am actually calling the function for the first time so it runs.
For cycle without cycleâs variable increment/decrement
function chunkArrayInGroups(arr, size) {
var ar = [];
for (i = 0; i < arr.length;) ar.push(arr.splice(i, size));
return ar;
}
chunkArrayInGroups([0, 1, 2, 3, 4, 5, 6, 7, 8], 4);
Hey lbarjak, I know the final-expression in a for statement is optional, but how does the loop know to continue incrementing or updating the counter variable?
// Using splice.
// Found splice very useful in this case.
function chunkArrayInGroups(arr, size) {
// Break it up.
var arr1=[];
while (arr.length>0) {
arr1.push (arr.splice(0,size));
}
return arr1;
}
chunkArrayInGroups(["a", "b", "c", "d", "e"], 3);
âŚ