Get all non-unique values (i.e.: duplicate/more than one occurrence) in an array

Easy-Peasy: How to Get All Non-Unique Values in an Array

Are you tired of manually checking for duplicate values in a JavaScript array? 🔄

Well, fret no more! 🛡️

In this blog post, we'll uncover the easiest way to detect and retrieve all those pesky non-unique values in your array 🕵️‍♀️ without the hassle of index-finding or tallying duplicate counts.

So, let's dive right in and get our array-game on! 💪

The Context

Our curious reader posed this intriguing question: "What's the easiest way to find duplicated values in a JavaScript array without the need for index information or counts?"

Good news! The JavaScript gurus have got you covered like a cozy array blanket. 🛌💤

The Solution 🌟

Introducing the Array.filter() method! 🆒🔍

This magical function allows us to create a new array with only the elements that pass a given test. And conveniently, with this test, we can easily identify non-unique values. 🎉

Here's the snippet to bring smiles to your array-detecting dreams:

const array = [1, 2, 3, 4, 1, 3, 5, 6];

const nonUniqueValues = array.filter((value, index, self) => self.indexOf(value) !== index);

console.log(nonUniqueValues); // [1, 3]

And voilà! 🎩

After applying the .filter() method along with a handy comparison of the index of each value, we swiftly retrieve all those duplicate entries. No indexes, no counting, just the non-unique values you've longed for! 😍

But wait, there's more! 📣

In the event that you have an array of objects or complex data structures, worry not my friend! 🚀

With a slight modification to our solution, you can conquer the arrays of objects too! 🏆

Here's an example using objects as array elements:

const people = [
  { name: 'John', age: 20 },
  { name: 'Jane', age: 30 },
  { name: 'John', age: 40 },
  { name: 'Jim', age: 20 },
];

const nonUniquePeople = people.filter((person, index, self) => 
  self.findIndex((p) => p.name === person.name) !== index
);

console.log(nonUniquePeople); 
// [
//   { name: 'John', age: 20 },
//   { name: 'John', age: 40 },
// ]

Boom! 💥

By combining .filter() with .findIndex(), we defeat the mighty object arrays too. We specifically target the duplicate objects based on a particular property, in this case, the name. Flex that array power! 💪

One Last Thing... 🛎️

Learning is great, but utilizing knowledge is even better! 💡

Now that you have the power to easily identify non-unique values in arrays, go forth and create amazing things! 🌟 Share your newfound wisdom, inspire others, and remember, there's always something new to explore in the realm of coding. 🚀

So, let's hear from you! Have you ever encountered a tricky array situation, and if so, how did you resolve it? Share your stories, tips, and tricks in the comments below, and let's level up together! 👇💬