groupBy(arr, key)

JavaScript

easy

5 mins

Write a function groupBy that takes an array of objects and a property name (as a string), and returns an object where the keys are the unique values of the specified property, and the values are arrays of objects that have that property value.

Example Inputs & Outputs

// Example 1:
const users = [
    { name: 'Alice', age: 25 },
    { name: 'Bob', age: 30 },
    { name: 'Charlie', age: 25 }
];
groupBy(users, 'age');
// Output: {
//     '25': [{ name: 'Alice', age: 25 }, { name: 'Charlie', age: 25 }],
//     '30': [{ name: 'Bob', age: 30 }]
// }

// Example 2:
const products = [
    { id: 1, category: 'Electronics' },
    { id: 2, category: 'Clothing' },
    { id: 3, category: 'Electronics' }
];
groupBy(products, 'category');
// Output: {
//     'Electronics': [{ id: 1, category: 'Electronics' }, { id: 3, category: 'Electronics' }],
//     'Clothing': [{ id: 2, category: 'Clothing' }]
// }

Constraints & Edge Cases

The input array may be empty, in this case return an empty object.
The key values can be of any type (number, string, etc.), but they will be coerced to strings when used as object keys.