Sorting array from given index

Question

Let's assume I have a simple array

const simpleArray = [1, 2, 3, 4, 5];

In case of, for example, I want to create a carousel and connect dots to click events in Vue or React. So clicking on a dot I want to sort my array so first slide will be the slide with the index of the dot. Hence if the index of the dot is 3 - my array should look like this now

const updatedSimpleArray = [3, 4, 5, 1, 2];

With this idea in mind I came to conclusion of creating this method.

const sortedArray = (pos) =>  {

  // pos is the dot index of the dot
  // if index is 1 - simply sort the array
  if ( pos == 1 ) return arr.sort();

  // otherwise - create two separate arrays and concat them
  const firstArr = arr.filter(el => el >= pos);
  const secondArr = arr.filter(el => el < pos);
  const newArr = [...firstArr, ...secondArr];
  return newArr;
}

What do you think about my approach and time/memory complexity? Would you use another approach?

EDIT

There is a problem if my array is not sorted. If it looks like this

const array = [4, 5, 1, 2, 3]

Whole function is not working correctly. My thoughts - sort it first and then filter/splice on given index?

Is there an actual problem? because if you're looking for an opinion about your approach then this is not the place. — Adrian
– Adrian, Commented Oct 4, 2019 at 11:45
This is for a slide carousel? If so, you don't need to do anything to your array. You'll keep a counter variable which will have a number representing the current index to show and simply increment or decrement that counter (depending on the direction the user wants to go) and check the counter to make sure it doesn't go out of bounds. — Scott Marcus
– Scott Marcus, Commented Oct 4, 2019 at 11:46
@ScottMarcus true, but I'm using vue with v-for approach, so to rerender the component I need to return modified array, I'm not jumping inside real dom. How would you implement react/vue approach with counter? Also my slider is here - fancy-slider.firebaseapp.com — Олег Якунин
– Олег Якунин, Commented Oct 4, 2019 at 12:41

Harish · Accepted Answer · 2019-10-04 12:00:27Z

4

You can do like, remove the elements from your index to length of the array and push it to start of the same array

    const array = [1, 2, 3, 4, 5];
    const index = 2;
    array.unshift(...array.splice(index))
    
    console.log(array)

answered Oct 4, 2019 at 12:00

Harish

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Comments

adiga · Accepted Answer · 2019-10-04 11:58:58Z

1

You could get the index of the current dot value. Then create an array with 2 iterations of the original array using [...array, ...array]. For the given array, it will look like [1, 2, 3, 4, 5, 1, 2, 3, 4, 5]. Then use slice to get array.length items starting from index

function getRotation(array, value) {
  const index = array.indexOf(value);
  return [...array, ...array].slice(index, index + array.length)
}

console.log(getRotation([1, 2, 3, 4, 5], 3))
console.log(getRotation([1, 2, 3, 4, 5], 5))

edited Oct 4, 2019 at 11:58

answered Oct 4, 2019 at 11:51

adiga

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1 Comment

Harry Joy Over a year ago

A good way to learn things, but less practical. Just image an array of 1000 elements or even more. you will just slowly explode the memory and processing by simply duplicating array and cutting it out.

Олег Якунин · Accepted Answer · 2019-10-04 12:37:30Z

1

Combining knowledge from Harish' answer I refactored the algorithm. Now it works with both examples, where arrays can look like this.

const array1 = [1, 2, 3, 4, 5]
const array2 = [4, 5, 1, 2, 3]

So here goes the function

const sortedArray = (pos) =>  {
  // First of all - sort the array
  const newArr = arr.sort((a, b) => a - b);

  // and then splice it and add this part to the start of the array
  newArr.unshift(...newArr.splice(pos-1));
  return newArr;
}

answered Oct 4, 2019 at 12:37

Олег Якунин

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