Move multiple array elements from one array position to another

Question

I need to move four items from an array of items to the first four positions.

Let say I have the below array:

var countryList=['Afghanistan','Albania', 'Argentina', 'Australia', 'Bangladesh', 'Belgium','Brazil',...]

I need to move Argentina, Australia, Belgium, and Brazil at first four positions. The modified array should look like:

var modifiedCountryList=['Argentina', 'Australia','Belgium', 'Brazil', 'Afghanistan', 'Albania', 'Bangladesh', ...]

I have found an answer here but it is for a single array element position move.

It seems like simple but I can not wrap my head around it.

What have you tried? What logic is used to select those particular values? How are they ordered? — RobG, Apr 21 '18 at 04:50
What are your inputs, if we solve this problem its going to be specific to your current input — Lasitha Petthawadu, Apr 21 '18 at 04:52
@RobG and @ Lasitha Petthawadu - All the below answers are working for my particular problem. — Shahid, Apr 21 '18 at 06:02

score 2 · Answer 1 · answered Apr 21 '18 at 05:53

2

You can array#concat both of your arrays. Using Set get the elements and place them in an array.

NOTE: Use of Set will remove the duplicate element, if any, in the result array.

const countryList=['Afghanistan','Albania', 'Argentina', 'Australia', 'Bangladesh', 'Belgium','Brazil'],
    first = ['Argentina', 'Australia','Belgium', 'Brazil'],
    result = [...new Set([].concat(first, countryList))];
console.log(result);

answered Apr 21 '18 at 05:53

Hassan Imam

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Thank you, @Hassan Imam! Your solution is working as expected. – Shahid Apr 21 '18 at 06:09

score 1 · Answer 2 · answered Apr 21 '18 at 04:50

1

Just make a new array with the desired countries in first and .filter out the matching elements in the first array:

const countryList1 = ['Afghanistan','Albania', 'Argentina', 'Australia', 'Bangladesh', 'Belgium','Brazil'];
const countriesInFirst = ['Argentina', 'Australia','Belgium', 'Brazil'];

const countryList2 = [
  ...countriesInFirst,
  ...countryList1.filter(country => !countriesInFirst.includes(country))
];
console.log(countryList2);

answered Apr 21 '18 at 04:50

CertainPerformance

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Thank you CertainPerformance! Your solution is working as expected. – Shahid Apr 21 '18 at 05:54

score 1 · Answer 3 · answered Apr 21 '18 at 05:01

1

var countryList=['Afghanistan','Albania', 'Argentina', 'Australia', 'Bangladesh', 'Belgium','Brazil'];

var filterArray = ["Argentina","Australia","Belgium","Brazil"];

var result = [...filterArray,...countryList].filter((v, i, a) => a.indexOf(v) === i);

console.log(result);

answered Apr 21 '18 at 05:01

Nishant Dixit

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Thank you, Nishant Dixit! Your solution is working as expected. – Shahid Apr 21 '18 at 05:56

score 1 · Answer 4 · answered Apr 21 '18 at 05:06

Simply, exclude the first countries from the list of countries and then concatenate the filtered list to the first countries' list:

const countries = ['Afghanistan','Albania', 'Argentina', 'Australia', 'Bangladesh', 'Belgium','Brazil'];
const first = ['Argentina', 'Australia','Belgium', 'Brazil'];

// Get the list of countries without first four countries
const filtered = countries.filter(country => !first.includes(country));

// Prepare the final list of countries
const c1 = first.concat(filtered);
console.log(c1);

Thank you 31piy! Your solution is working as expected. – Shahid Apr 21 '18 at 05:53 — Shahid, Apr 21 '18 at 05:53

score 1 · Accepted Answer · edited Apr 21 '18 at 07:17

Make a new array with the output you expect. Also, I would suggest to use indexOf instead of includes as includes will give you error in IE browser. You can also make use of spread syntax ... that will add the array elements to your new array.

const countryList1 = ['Afghanistan','Albania', 'Argentina', 'Australia', 'Bangladesh', 'Belgium','Brazil'];
const countriesInFirst = ['Argentina', 'Australia','Belgium', 'Brazil'];

const countryList2 = [
  ...countriesInFirst,
  ...countryList1.filter(country => countriesInFirst.indexOf(country) === -1)
];
console.log(countryList2);

includes() is not supported in IE browser. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/includes#Browser_compatibility

Thank you, Ankit! your solution is working as expected – Shahid Apr 21 '18 at 05:52 — Shahid, Apr 21 '18 at 05:52

Move multiple array elements from one array position to another

5 Answers5