Bits of .NET

📊 _.groupBy() is Finally Native

Grouping arrays required Lodash or manual reduce. Object.groupBy() is native. No more dependencies.

📝 Basic GroupBy

const users = [
  { name: 'Alice', role: 'admin' },
  { name: 'Bob', role: 'user' },
  { name: 'Charlie', role: 'admin' }
];

const byRole = Object.groupBy(users, user => user.role);
// {
//   admin: [{ name: 'Alice' }, { name: 'Charlie' }],
//   user: [{ name: 'Bob' }]
// }

const byFirstLetter = Object.groupBy(['apple', 'banana', 'apricot'], word => word[0]);
// { a: ['apple', 'apricot'], b: ['banana'] }

🎯 Real-World Examples

// Group orders by date
const orders = [
  { id: 1, date: '2024-01-15', total: 100 },
  { id: 2, date: '2024-01-15', total: 200 },
  { id: 3, date: '2024-01-16', total: 150 }
];

const byDate = Object.groupBy(orders, order => order.date);
// Use byDate['2024-01-15'] to get orders from that day

// Group by age bracket
const people = [
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: 32 },
  { name: 'Charlie', age: 28 }
];

const byAgeGroup = Object.groupBy(people, p => {
  if (p.age < 30) return '20s';
  if (p.age < 40) return '30s';
  return '40+';
});

💡 Map.groupBy for Maps

• Object.groupBy: Returns plain object (string keys)
• Map.groupBy: Returns Map (any key type, preserves order)
• Use Map.groupBy when keys are numbers, booleans, or objects