Suppose I have the following code:
let array = [[1,2,3],[1,3,2],[2,3,1],[1,2,3],[2,4,5]]array = [[1,2,3],[2,4,5]]. The inner array with the most occurrence should be on top of the new array.How to I do that?
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3 Answers
Sort them, and use a Set for duplicates:
const dupes = new Set();
const result = array.filter(arr => {
const key = arr.sort().join("_");
return !dupes.has(key) && dupes.add(key);
});
To sort them after their appearances, we have to count the appearances in the original array, then sort:
const appeared = new Map();
const result = array.filter(arr => {
const key = arr.sort().join("_");
return !appeared.has(key) && appeared.set(key, (appeared.get(key) || 0) + 1);
}).sort((a, b) => appeared.get(a.join("_")) - appeared.get(b.join("_")));
6 Comments
Elon Musk
Thanks for your answer. However, I need the result to be an array, not a set. How do I do that?
Jonas Wilms
@yuvraj the result is an array?
Elon Musk
Do you have any idea on how to make the most popular item appear on top of the new array?
Jonas Wilms
@yuvraj sure, but thats not part of the question (yet)
Elon Musk
I edited the question, I will wait for your answer. Thank you again.
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✓ @yuvraj, you can solve this problem by using the concept of Set() and join(), split(), map(), sort() methods.
Set() may be a new concept for new JavaScript programmers. Here is an article as Sets in JavaScript - GeeksforGeeks which has a clear, nice and brief explanation for the Sets().
✓ Here, I have tried to show this step by step with a simple example.
Please comment if the code example doesn't satisfy your need. I will update the based on your provided inputs and expected outputs.
Here at http://rextester.com/AVPXM70965, you can find the code on online IDE.
var a = [1, 2, 3]
var b = [1, 2, 3]
var c = [3, 2, 1]
console.log(a.join("") === b.join("")) // true
console.log(a.join("") === c.join("")) // false
console.log(a.join("") === c.sort().join("")) // true
console.log(a.sort().join("") === c.sort().join("")) // true
✓ Finally
var array = [[1,2,3],[1,3,2],[2,3,1],[1,2,3],[2,4,5]]
texts = array.map((arr) => arr.sort().join(":"))
console.log(texts)
var unique_texts = new Set(texts)
console.log(unique_texts)
/*
[ '1:2:3', '1:2:3', '1:2:3', '1:2:3', '2:4:5' ]
Set { '1:2:3', '2:4:5' }
*/
var new_array = []
unique_texts.forEach((item) => {
var arr = item.split(":").map(num => parseInt(num))
new_array.push(arr)
})
console.log(new_array)
// [ [ 1, 2, 3 ], [ 2, 4, 5 ] ]
Comments
Essentially you need a counter and a bit of code to get the key, value pairs back to an array. Lodash has an implementation of a counter and a lot of other useful functions.
let array = [
[1, 2, 3],
[1, 3, 2],
[2, 3, 1],
[1, 2, 3],
[2, 4, 5]
];
// count by the sorted elements
const counter = _.countBy(array, inner => inner.slice().sort());
// counter is of form: {"2,4,5":1, ...}
// let's use lodash to make an array of [key, value] pairs
const pairs = _.toPairs(counter);
// sort by desc popularity (hence the minus)
const sortedByPopularity = _.sortBy(pairs, pair => -pair[1]);
// convert the "1,2,3" keys back to arrays of numbers
const result = sortedByPopularity.map(pair => pair[0].split(',').map(Number));
console.log(result);<script src="https://cdn.jsdelivr.net/npm/[email protected]/lodash.min.js"></script>