Function groupBy

groupBy<const Ar extends readonly unknown[], G extends Primitive>(
array: Ar,
grouper: (value: Ar[number], index: ArrayIndex<Ar>) => G,
): IMap<G, readonly Ar[number][]>

Groups elements by a key derived from each element.

Type Parameters

const Ar extends readonly unknown[]
G extends Primitive

Parameters

array: Ar
grouper: (value: Ar[number], index: ArrayIndex<Ar>) => G

Returns IMap<G, readonly Ar[number][]>

Example

const animals = ['ant', 'bat', 'cat', 'dove'] as const;

const groupedByLength = Arr.groupBy(animals, (animal) => animal.length);
const groupedByFirstLetter = Arr.groupBy((animal: string) => animal[0])(
  animals,
);

assert.deepStrictEqual(
  groupedByLength.get(3),
  Optional.some(['ant', 'bat', 'cat'] as const),
);
assert.deepStrictEqual(
  groupedByLength.get(4),
  Optional.some(['dove'] as const),
);
assert.deepStrictEqual(groupedByLength.get(5), Optional.none);

assert.deepStrictEqual(
  groupedByFirstLetter.get('a'),
  Optional.some(['ant'] as const),
);
assert.deepStrictEqual(
  groupedByFirstLetter.get('d'),
  Optional.some(['dove'] as const),
);

groupBy<E, G extends Primitive>(
grouper: (value: E, index: Uint32) => G,
): (array: readonly E[]) => IMap<G, readonly E[]>

Groups elements by a key derived from each element.

Type Parameters

E
G extends Primitive

Parameters

grouper: (value: E, index: Uint32) => G

Returns (array: readonly E[]) => IMap<G, readonly E[]>

Example

const animals = ['ant', 'bat', 'cat', 'dove'] as const;

const groupedByLength = Arr.groupBy(animals, (animal) => animal.length);
const groupedByFirstLetter = Arr.groupBy((animal: string) => animal[0])(
  animals,
);

assert.deepStrictEqual(
  groupedByLength.get(3),
  Optional.some(['ant', 'bat', 'cat'] as const),
);
assert.deepStrictEqual(
  groupedByLength.get(4),
  Optional.some(['dove'] as const),
);
assert.deepStrictEqual(groupedByLength.get(5), Optional.none);

assert.deepStrictEqual(
  groupedByFirstLetter.get('a'),
  Optional.some(['ant'] as const),
);
assert.deepStrictEqual(
  groupedByFirstLetter.get('d'),
  Optional.some(['dove'] as const),
);

Function groupBy

Type Parameters

Parameters

Returns IMap<G, readonly Ar[number][]>

Example

Type Parameters

Parameters

Returns (array: readonly E[]) => IMap<G, readonly E[]>

Example

Settings