Utilizing sorted array indices in reference to the original array (JavaScript)

Question

Utilizing sorted array indices in reference to the original array (JavaScript)

Imagine you have a randomly arranged array of day strings like:

var days = ['Tues', 'Thur', 'Mon', 'Wed']

where days[0] = 'Tues', days[1] = 'Thurs', and so on. When you sort this array, it becomes

sortedDays = ['Mon', 'Tues', 'Wed', 'Thur']

But now, the challenge is to associate the indices of the newly-sorted array with those of the original array; for example, the old array has indices as (0, 1, 2, 3) while the new array has indices as (2, 0, 3, 1).

Figuring out how to accomplish this task can be tricky.

javascript arrays sorting

Answer 1

Answer №1

Utilize the Array.prototype.indexOf() method to locate the position (index) of an element in an array. You can execute .indexOf() on each element within your sortedDays array.

const days = ['Tues', 'Thur', 'Mon', 'Wed'];
const sortedDays = ['Mon', 'Tues', 'Wed', 'Thur'];
const sortedDaysIndices = sortedDays.map(day => days.indexOf(day));
console.log(sortedDaysIndices);

Answer 2

Utilize the Array.prototype.indexOf() method to locate the position (index) of an element in an array. You can execute .indexOf() on each element within your sortedDays array.

const days = ['Tues', 'Thur', 'Mon', 'Wed'];
const sortedDays = ['Mon', 'Tues', 'Wed', 'Thur'];
const sortedDaysIndices = sortedDays.map(day => days.indexOf(day));
console.log(sortedDaysIndices);

Answer 3

Answer №2

To obtain the sorted indexes, one can initialize an array from [0...n] and then arrange that array based on the days' sorting order.

For instance:

// Defines the sorting order for days:
const sortDays = {
    Mon:  0,
    Tues: 1, 
    Wed:  2,
    Thur: 3,
    Fri:  4,
    Sat:  5,
    Sun:  6
}

const days = ['Tues', 'Thur', 'Mon', 'Wed', 'Thur', 'Sun', 'Mon'];
// original indices
let index = Array.from(days, (_,i) => i)
index.sort((a, b) => sortDays[days[a]] - sortDays[days[b]])

// the indices are now sorted according to the days' sort order
console.log("indices: ", index.join(','))

// use the index to sort the days:
sortedDays = index.map(i => days[i])
console.log("sorted days:", sortedDays.join(','))

This method ensures that you get the correct indices even with duplicates in the initial list.

Answer 4

To obtain the sorted indexes, one can initialize an array from [0...n] and then arrange that array based on the days' sorting order.

For instance:

// Defines the sorting order for days:
const sortDays = {
    Mon:  0,
    Tues: 1, 
    Wed:  2,
    Thur: 3,
    Fri:  4,
    Sat:  5,
    Sun:  6
}

const days = ['Tues', 'Thur', 'Mon', 'Wed', 'Thur', 'Sun', 'Mon'];
// original indices
let index = Array.from(days, (_,i) => i)
index.sort((a, b) => sortDays[days[a]] - sortDays[days[b]])

// the indices are now sorted according to the days' sort order
console.log("indices: ", index.join(','))

// use the index to sort the days:
sortedDays = index.map(i => days[i])
console.log("sorted days:", sortedDays.join(','))

This method ensures that you get the correct indices even with duplicates in the initial list.

Answer 5

Answer №3

const weekdays = ['Tuesday', 'Thursday', 'Monday', 'Wednesday'];

const sortedWeekdays = ['Monday', 'Tuesday', 'Wednesday', 'Thursday'];

const indexMapping = {}
weekdays.forEach((day, idx)=> (indexMapping[day] = { 
    oldIdx: idx  , newIdx: sortedWeekdays.indexOf(day)}
 )
)

console.log(indexMapping)

Answer 6

const weekdays = ['Tuesday', 'Thursday', 'Monday', 'Wednesday'];

const sortedWeekdays = ['Monday', 'Tuesday', 'Wednesday', 'Thursday'];

const indexMapping = {}
weekdays.forEach((day, idx)=> (indexMapping[day] = { 
    oldIdx: idx  , newIdx: sortedWeekdays.indexOf(day)}
 )
)

console.log(indexMapping)

Utilizing sorted array indices in reference to the original array (JavaScript)

Answer №1

Answer №2

Answer №3

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