Function groupBy

groupBy<K extends string, T extends Record<K, string | number>>(
array: T[],
key: K,
): { [key: string]: T[] }

Groups an array of objects by the value of a specified property. Creates a new object where each key represents a unique value from the specified property, and each value is an array of objects that have that property value. Uses immutable operations to avoid mutating the original array.

Type Parameters

K extends string
T extends Record<K, string | number>

Parameters

array: T[]
The array of objects to group
key: K
The property name to group by (must exist on all objects and have string or number values)

Returns { [key: string]: T[] }

An object where keys are the unique property values and values are arrays of matching objects

Example

const employees = [
  { name: 'John', department: 'Engineering', salary: 75000 },
  { name: 'Jane', department: 'Marketing', salary: 65000 },
  { name: 'Bob', department: 'Engineering', salary: 80000 },
  { name: 'Alice', department: 'Marketing', salary: 70000 }
];

const byDepartment = groupBy(employees, 'department');
// Result: {
//   'Engineering': [
//     { name: 'John', department: 'Engineering', salary: 75000 },
//     { name: 'Bob', department: 'Engineering', salary: 80000 }
//   ],
//   'Marketing': [
//     { name: 'Jane', department: 'Marketing', salary: 65000 },
//     { name: 'Alice', department: 'Marketing', salary: 70000 }
//   ]
// }

// Group by numeric values
const products = [
  { name: 'Laptop', price: 1000, category: 1 },
  { name: 'Mouse', price: 25, category: 1 },
  { name: 'Desk', price: 300, category: 2 }
];
const byCategory = groupBy(products, 'category');
// Groups by category: { '1': [...], '2': [...] }

Since

1.0.0