How to get sequential elements from Javascript array?

Question

I have this Javascript array:

var cars = ["Saab", "Volvo", "BMW", "Volkswagen", "Fiat"];

I know that I can get each of these elements by index like this:

cars[2] // => "BMW"

But how can I get three sequential elements at once?

getThreeCarsByIndex(4) // => ["Fiat", "Saab", "Volvo"]

Thanks for your help.

Answer 1

Just use simple modular arithmetic-

const cars = ["Saab", "Volvo", "BMW", "Volkswagen", "Fiat"];

function getThreeCarsByIndex(ix) {
    return [0, 1, 2].map(offset => cars[(ix + offset) % cars.length]);
}

console.log(getThreeCarsByIndex(4));

When cars.length is 5, 4 % cars.length gives you 4, 5 % cars.length wraps it back to 0 and so on

Oh and also here's a general version because why not-

function getXElementsFrom(start, x, arr) {
    return [...Array(x).keys()].map(offset => arr[(start + offset) % arr.length]);
}

const cars = ["Saab", "Volvo", "BMW", "Volkswagen", "Fiat"];

console.log(getXElementsFrom(4, 3, cars));

[...Array(x).keys()] is basically the equivalent of range(x) in languages like python.

Answer 2

Use modulo operator to get the desired index without being out of range.

function getThreeCarsByIndex(array, index)
{
  const result = [];
  
  for (let i = 0; i < 3; i++)
  {
    result.push(array[(index + i) % array.length]);
  }
  
  return result;
}

var cars = ["Saab", "Volvo", "BMW", "Volkswagen", "Fiat"];

console.log(getThreeCarsByIndex(cars, 4));

Answer 3

Here is one approach

const cars = ["Saab", "Volvo", "BMW", "Volkswagen", "Fiat"];

const getThreeCarsByIndex = (index) => cars.slice(index, index + 3).concat(cars.slice(0, (index + 1) % 3))

console.log(getThreeCarsByIndex(4))

Answer 4

Use slice. If length is not met (3 here), grab the remaining elements from array begin

const getThreeCarsByIndex = (arr, index) => {
  const res = arr.slice(index, index + 3);
  return res.concat(arr.slice(0, 3 - res.length));
};

var cars = ["Saab", "Volvo", "BMW", "Volkswagen", "Fiat"];

console.log(getThreeCarsByIndex(cars, 4))

Answer 5

You can define a custom function and check whether the given count + given index is greater than length of the array

const getElementsFromIndex = (arr, ind, n) => {
  if(n + ind > arr.length - 1){
    let elementsFromStart = ind + n - arr.length + 1;
    console.log(elementsFromStart)
    return arr.slice(ind).concat(arr.slice(0, elementsFromStart))
  }
  else return arr.slice(ind, ind + n);
}


const arr = [1,2,3,4,5];
console.log(getElementsFromIndex(arr, 4, 3))

Answer 6

var cars = ["Saab", "Volvo", "BMW", "Volkswagen", "Fiat", "Saab", "Volvo"];

cars.slice(4, 7); // => ["Fiat", "Saab", "Volvo"]

Answer 7

It's enough just to write

cars.sort().slice(1,4);

Of course you can create a function that will work for other arrays as well, e.g.

let cars = ["Saab", "Volvo", "BMW", "Volkswagen", "Fiat"];
    
getSequentionalElements = (arr, firstElement, lastElement) => arr.sort().slice(firstElement, lastElement)

let newArray = getSequentionalElements(cars, 1, 4)

console.log(newArray);