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

user_5490549 0
Viewed 3302

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?

substring arrays javascript
6 Answers

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; }

user_14476750

You have two issues in your code:

  1. 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
  2. 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);
  }
}

user_70531900

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);            
          }  
        }

user_59463160

Use two iteration

  1. get slice array based on loop index.
  2. 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))

user_4609420

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();
};
// [...]
user_94834050
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);
user_70708080
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