Includes function for Array of Array

Question

I have an array of array.

m = [[-100,100], [-100,-100], [-100,-100], [-100,100]]

And I want to remove the duplicates. I tried

 aa = [...new Set(m)];

// and 

let chkdup = (arr, tar) => tar.every(v => arr.includes(v))`.

But I can't remove the duplicates.

In Python, I can easily check this [-100,100] in m. But I don't know the function in JS. includes is not working for this case.

score 2 · Answer 1 · answered Jan 11 '21 at 11:36

This happens because [-100, 100] != [-100, 100]. What you can do is convert the arrays into strings, and compare the strings instead, with JSON.stringify.

let m = [[-100,100], [-100,-100], [-100,-100], [-100,100]]
m = m.map(item => JSON.stringify(item).trim()) // Stringify everything (remove leading white space)
m = [...new Set(m)] // Convert to array getting rid of duplicates
m = m.map(item => JSON.parse(item)) // Parse it

Note that this is not very efficient (The interpreter has to convert into a string and parse the object again) but it is the simpliest solution. What it does is it checks if the JSON string of 2 Objects is equal an will not work with your own classes.

Mark · Accepted Answer · 2021-01-11T12:54:57.270

The reason why new Set doesn't work well is because in JavaScript, arrays with the same values are not equal. Try: console.log([-100,100] == [-100,100]); will return false. Please refer to this post if you simply wants to compare between arrays.

A workaround is to convert subarrays into strings, and use Set to deduplicate:

const arr = [
  [-100, 100],
  [-100, -100],
  [-100, -100],
  [-100, 100]
];

const setArray = new Set(arr.map(x => JSON.stringify(x)));

const result = [...setArray].map(x => JSON.parse(x));

console.log(result);

Using lodash uniq is a simple alternative.

score 1 · Answer 3 · answered Jan 11 '21 at 11:46

You can simply do this thing using javascript Set , map then parse the value. For more information Map with Set

 m = [[-100,100], [-100,-100], [-100,-100], [-100,100]];
 result = Array.from(new Set(m.map(JSON.stringify)), JSON.parse);
 console.log(t);

score 1 · Answer 4 · answered Jan 11 '21 at 11:46

You can stringify your arrays using .map() with JSON.stringify(), and enter that into a set. Since you now have an array of strings, the set will remove the duplicates as it can check for equality correctly. You can then use Array.from with a mapping function of JSON.parse to convert it back into an array of arrays:

const m = [[-100,100], [-100,-100], [-100,-100], [-100,100]];
const res = Array.from(new Set(m.map(JSON.stringify)), JSON.parse);
console.log(res);

Includes function for Array of Array

4 Answers4