JavaScript: Get all unique values of an array, based on a provided comparator function

JavaScript fundamental (ES6 Syntax): Exercise-108 with Solution

Unique Values by Comparator

Write a JavaScript program to get all unique values of an array, based on a provided comparator function.

• Use Array.prototype.reduce() and Array.prototype.some() for an array containing only the first unique occurrence of each value, based on the comparator function, fn.
• The comparator function takes two arguments: the values of the two elements being compared.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2

// Define a function 'uniqueElementsBy' to return unique elements from an array based on a comparison function.
const uniqueElementsBy = (arr, fn) =>
  // Use reduce to iterate over the array 'arr'.
  arr.reduce((acc, v) => {
    // If the accumulator 'acc' does not contain any element that satisfies the comparison function 'fn' with the current element 'v', add 'v' to the accumulator.
    if (!acc.some(x => fn(v, x))) acc.push(v);
    // Return the accumulator.
    return acc;
  }, []);

// Test the 'uniqueElementsBy' function with an example.
console.log(uniqueElementsBy(
  [
    { 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
));  

Output:

[{"id":0,"value":"a"},{"id":1,"value":"b"},{"id":2,"value":"c"}]

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-108-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that returns an array of unique values from the input array based on a provided comparator function.
• Write a JavaScript function that checks for uniqueness of elements using a comparator and returns the filtered array.
• Write a JavaScript program that iterates over an array and removes duplicates by comparing each element with a custom equality function.

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