JavaScript: Filter out the non-unique values in an array, based on a provided comparator function

JavaScript fundamental (ES6 Syntax): Exercise-23 with Solution

Write a JavaScript program to filter out non-unique values in an array, based on a provided comparator function.

Note: The comparator function takes four arguments: the values of the two elements being compared and their indexes.

• Use Array.prototype.filter() and Array.prototype.every() to create an array containing only the unique values, based on the comparator function, fn.
• The comparator function takes four arguments: the values of the two elements being compared and their indexes.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
// Define a function called `filter_Non_UniqueBy` that filters an array of objects based on a provided comparison function.
const filter_Non_UniqueBy = (arr, fn) =>
  arr.filter((v, i) => arr.every((x, j) => (i === j) === fn(v, x, i, j)));

// Example usage
console.log(filter_Non_UniqueBy(
  [
    { id: 0, value: 'a' },
    { id: 1, value: 'b' },
    { id: 2, value: 'c' },
    { id: 1, value: 'd' },
    { id: 0, value: 'e' }
  ],
  (a, b) => a.id == b.id
)); // [{ id: 2, value: 'c' }]

Output:

[{"id":2,"value":"c"}]

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-1-23 by w3resource (@w3resource) on CodePen.

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