Description

groupBy takes an array of objects and a key (string), and returns an object where each distinct value of that key in the array becomes a property. The corresponding value is an array of all objects from the input that share that key value.

Code Byte

export const groupBy = <T extends Record<string, any>, K extends keyof T>(
  arr: T[],
  key: K
): Record<string, T[]>  =>{
  return arr.reduce((acc: Record<string, T[]>, obj: T) => {
    const groupKey = String(obj[key]);
    acc[groupKey] = acc[groupKey] || [];
    acc[groupKey].push(obj);
    return acc;
  }, {});
}

Use cases:

• Data categorization: Group users by role, products by category, etc.
• Analytics aggregation: Bucket events by event type or date.
• UI rendering: Render sectioned lists grouped by a property (e.g., year, status).
• Batch processing: Partition items before processing each group separately.

Example usage:

import { groupBy } from './group-by.util';

interface User {
  id: number;
  name: string;
  role: string;
}

const users: User[] = [
  { id: 1, name: 'Alice', role: 'admin' },
  { id: 2, name: 'Bob', role: 'user' },
  { id: 3, name: 'Eve', role: 'admin' },
  { id: 4, name: 'Mallory', role: 'user' }
];

const usersByRole = groupBy(users, 'role');

console.log(usersByRole);
/*
{
  admin: [
    { id: 1, name: 'Alice', role: 'admin' },
    { id: 3, name: 'Eve', role: 'admin' }
  ],
  user: [
    { id: 2, name: 'Bob', role: 'user' },
    { id: 4, name: 'Mallory', role: 'user' }
  ]
}
*/