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.
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.
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));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))
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))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))
var cars = ["Saab", "Volvo", "BMW", "Volkswagen", "Fiat", "Saab", "Volvo"];
cars.slice(4, 7); // => ["Fiat", "Saab", "Volvo"]
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);
4 % cars.length,(4 + 1) % cars.length,(4 + 2) % cars.length