Unique Values in Array Based on Function

Introduction

In this lab, we will explore a JavaScript function that helps find all unique values in an array based on a provided comparator function. We will use the Array.prototype.reduce() and Array.prototype.some() methods to create a new array that contains only the first unique occurrence of each value, based on the provided comparator function. This lab will provide you with a deeper understanding of how to manipulate arrays in JavaScript.

Skills Graph

Finding Unique Values in an Array with a Function

To find all unique values of an array, provide a comparator function.

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

const uniqueElementsBy = (arr, fn) =>
  arr.reduce((acc, v) => {
    if (!acc.some((x) => fn(v, x))) acc.push(v);
    return acc;
  }, []);

To test the function, use the example below:

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
); // [ { id: 0, value: 'a' }, { id: 1, value: 'b' }, { id: 2, value: 'c' } ]

Start practicing coding by opening the Terminal/SSH and typing node.

Summary

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