I have an array with 8 elements. How do I move the last 4 elements to the front?
- 2What have you tried so far?evolutionxbox– evolutionxbox2022-05-10 09:17:11 +00:00Commented May 10, 2022 at 9:17
- I have tried using splice. But It is a bit confusing, also tried to use pushing new items and then unshifting them, but only 1 element moves to the start, no idea how to move more than one. (I am currently learning about Arrays so no prior knowledge).Danyerden– Danyerden2022-05-10 09:19:22 +00:00Commented May 10, 2022 at 9:19
- 1Both slice and splice can move more than one item at a timeevolutionxbox– evolutionxbox2022-05-10 09:20:12 +00:00Commented May 10, 2022 at 9:20
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3 Answers
You can use Array.prototype.concat() combined with Array.prototype.slice():
const arr = [1, 2, 3, 4, 5, 6, 7, 8] const result = arr.slice(4).concat(arr.slice(0, 4)) console.log(result)A more dynamic version:
const arr = [1, 2, 3, 4, 5, 6, 7, 8] const half = arr.length / 2 const result = arr.slice(half).concat(arr.slice(0, half)) console.log(result)5 Comments
Craig Wayne
i was just wondering why you used
concat instead of the spread operator.... the concat method is much better performance wise. see stackoverflow.com/questions/48865710/…. Good job :)
Yosvel Quintero
For performance
Yosvel Quintero
@CraigWayne Thank you for your comment.. Checking on the link
Danyerden
Found this very helpful, now I understand how to move things around. Appreciated!
Yosvel Quintero
@Danyerden Good to help
You can use a combination of the Array.prototype.slice method and the Spread operator.
First spread the last four elements from the original array and then spread the remaining elements from the beginning.
const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], newArr = [...arr.slice(-4), ...arr.slice(0, -4)]; console.log(newArr);You can also do it by just using Array.prototype.Splice but remember it mutates the original array.
const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]; arr.splice(0, 0, ...arr.splice(-4)); console.log(arr); answered May 10, 2022 at 9:22
Som Shekhar Mukherjee
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Comments
If you're ok mutating the array (rather than creating a new one) splice the last four elements, and then unshift them to the start of the array.
(Note: splice returns an array, so you need to spread the elements out.)
const arr = [1, 2, 3, 4, 5, 6, 7, 8]; arr.unshift(...arr.splice(-4)); console.log(arr);
3 Comments
Yosvel Quintero
This solution mutates
arr
Andy
I'm ok with that.
Som Shekhar Mukherjee
This is nice +1, I came up with
arr.splice(0, 0, ...arr.splice(-4))