Say I have an array like so:
let arr = [1, 2, 3, 4, 5, 6, "a"]
How can I deconstruct it in into individual variables in increments of two? So that let one = [1, 2], let two = [3, 4], etc? I know that you can deconstruct an array using individual variables like so:
let one, two, three;
[one, two, three] = arr
But doing it in increments of two, is that possible?
Say I have an array like so:
let arr = [1, 2, 3, 4, 5, 6, "a"]
How can I deconstruct it in into individual variables in increments of two? So that let one = [1, 2], let two = [3, 4], etc? I know that you can deconstruct an array using individual variables like so:
let one, two, three;
[one, two, three] = arr
But doing it in increments of two, is that possible?
Share Improve this question asked Jun 21, 2019 at 18:12 JimmyNeedlesJimmyNeedles 1611 silver badge8 bronze badges 1- In a single destructuring statement? No, you'd need an intermediate step. – zero298 Commented Jun 21, 2019 at 18:16
6 Answers
Reset to default 7Another way you could do this is via ES6 generator function:
let arr = [1, 2, 3, 4, 5, 6, 'a']
function* batch (arr, n=2) {
let index = 0
while (index < arr.length) {
yield arr.slice(index, index + n)
index += n
}
}
let [first, second, third] = batch(arr)
console.log(first)
console.log(second)
console.log(third)Or even more generic approach as kindly suggested by @Patrick Roberts:
let arr = [1, 2, 3, 4, 5, 6, 'a']
function* batch (iterable, length=2) {
let array = [];
for (const value of iterable) {
if (array.push(value) === length) {
yield array;
array = [];
}
}
if (array.length) yield array;
}
let [first, second, third] = batch(arr);
console.log(first)
console.log(second)
console.log(third)And finally a curried version:
let arr = [1, 2, 3, 4, 5, 6, 'a']
const batch = length => function* (iterable) {
let array = [];
for (const value of iterable) {
if (array.push(value) === length) {
yield array;
array = [];
}
}
if (array.length) yield array;
}
let [first, second, third] = batch(2)(arr);
console.log(first)
console.log(second)
console.log(third)You could take an array and assign the value to the explicit target.
An automatic assignment is on the left hand side not possible by using a spread syntax with arrays with a length of two.
let array = [1, 2, 3, 4, 5, 6, "a"],
one = [], two = [], three = [];
[one[0], one[1], two[0], two[1], three[0], three[1]] = array;
console.log(one);
console.log(two);
console.log(three);.flatMap() is a bination of .map() and .flat() it allows the callback to skip returning values, return a value, and return multiple values which is made possible by returning arrays which get flattened in the final step. This demo has a callback which is a ternary that returns 2 values in an array every other iteration while it returns an empty array on alternating iterations. The result is an array of arrays which is then destructured.
let arr = [1, 2, 3, 4, 5, 6, "a"];
let newArr = arr.flatMap((node, index, array) => index % 2 !== 0 ? [
[array[index - 1], node]
] : []);
let [A, B, C] = newArr;
console.log(A);
console.log(B);
console.log(C);You can do that in following steps:
- Use
reduce()on the array and set accumulator to[] - During each iteration check the current index is divisible by the given number(
2). - If it does then add an empty array to the end to accumulator.
- Add the current element to the last subarray of accumulator each time.
let arr = [1, 2, 3, 4, 5, 6, "a"];
let [first,second,third] = arr.reduce((ac,a,i) => {
if(i % 2 === 0){
ac.push([]);
}
ac[ac.length - 1].push(a);
return ac;
},[])
console.log(first);
console.log(second);
console.log(third);Here is another curried version using a Generator, but this one uses Array.splice() to yield the values:
let arr = [1, 2, 3, 4, 5, 6, 'a'];
const getChunk = (len) => function * (arr)
{
arr = arr.slice(0);
while (arr.length >= len)
yield arr.splice(0, len);
yield arr;
}
let [one, two, three, four] = getChunk(2)(arr);
console.log("Chunks of size 2 =>", JSON.stringify([one, two, three, four]));
[one, two, three, four] = getChunk(3)(arr);
console.log("Chunks of size 3 =>", JSON.stringify([one, two, three, four]));
[one, two, three, four] = getChunk(1)(arr);
console.log("Chunks of size 1 =>", JSON.stringify([one, two, three, four]));.as-console {background-color:black !important; color:lime;}
.as-console-wrapper {max-height:100% !important; top:0;}is that possible?
Most anything is possible with coding.
let group = (arr, count) =>
arr.reduce((acc, v) => {
let last = acc[acc.length - 1];
if (last.length < count)
last.push(v);
else
acc.push([v]);
return acc;
}, [[]]);
let arr = [1, 2, 3, 4, 5, 6, "a"]
console.log(group(arr, 2));
console.log(group(arr, 3));
console.log(group(arr, 5));