How to get all substrings (contiguous subsequences) of my JavaScript array?

My task is to split the given array into smaller arrays using JavaScript. For example [1, 2, 3, 4] should be split to [1] [1, 2] [1, 2, 3] [1, 2, 3, 4] [2] [2, 3] [2, 3, 4] [3] [3, 4] [4].

I am using this code:



let arr = [1, 2, 3, 4];

for (let i = 1; i <= arr.length; i++) {
let a = [];
for (let j = 0; j < arr.length; j++) {
a.push(arr[j]);
if (a.length === i) {
break;
}
}
console.log(a);
}




And I get the following result: [1] [1, 2] [1, 2, 3] [1, 2, 3, 4] undefined

What am I missing/doing wrong?

You have two issues in your code:


You need to have loop to initialize with the value of i for the inner loop so that it consider the next index for new iteration of i
You need to remove that break on the length which you have in inner loop.




let arr = [1, 2, 3, 4];
for (let i = 0; i <= arr.length; i++) {
let a = [];
for (let j = i; j < arr.length; j++) {
a.push(arr[j]);
console.log(a);
}
}




For the inner array, you could just start with the index of the outer array.



var array = [1, 2, 3, 4],
i, j, l = array.length,
result = [];

for (i = 0; i < l; i++) {
for (j = i; j < l; j++) {
result.push(array.slice(i, j + 1));
}
}
console.log(result.map(a => a.join(' ')));
.as-console-wrapper { max-height: 100% !important; top: 0; }




Try this



let arr = [1, 2, 3, 4];
for (let i = 0; i <= arr.length; i++) {
let a = [];
for (let j = i; j < arr.length; j++) {
a.push(arr[j]);
console.log(a);
}
}




If you don't want to mutate your array.

let arr = [1, 2, 3, 4];
let res = [];
for (let i = 0; i <= arr.length; i++) {
let a = [];
for (let j = i; j < arr.length; j++) {
a = [...a, arr[j]];
res = [...res, a];
}
}
console.log(res);


i have prepare stackblitz for this case.

let source = [1,2,3,4];
const output = [];
const arrayMultiplier = (source) => {
const eachValueArray = [];
source.forEach((item, index) => {
// Will push new array who will be sliced source array.
eachValueArray.push(source.slice(0, source.length - index));
});
//We reverse array to have right order.
return eachValueArray.reverse();
};

for(let i = 0; i <= source.length; i++) {
output.push(...arrayMultiplier(source));
source.shift(); // Will recraft source array by removing first index.
}
//Don't forget last item.
output.push(source);
console.log(output);


Is not the most shorten solution but do the job

== update after code review ==

// [...]
const arrayMultiplier = (source) => {
// Will push new array who will be sliced source array.
// We reverse array to have right order.
return source.map((item, index) => source.slice(0, source.length - index)).reverse();
};
// [...]


Use two iteration


get slice array based on loop index.
use sliced array and combine array element.




var arr = [1, 2, 3, 4];
let newArra =[];
arr.map((x,i)=> {
let remainArr = arr.slice(i);
return remainArr.forEach((y, r) => newArra.push(remainArr.slice(0, r+1)))
})
newArra.forEach(x=> console.log(x))