Type Alias GroupBy<T, K>

GroupBy: {
    [Key in T[K] extends PropertyKey ? T[K] : never]: T extends T
        ? Key extends T[K] ? T : never
        : never
}

Groups a type T by the values of a key K.

Type Parameters

T
The target type (typically a union of objects)
K extends KeyOfType<T, PropertyKey>
The key to group by (must be a key of T with a PropertyKey type)

Example

type Apple = {
	type: "fruit";
	color: "green";
};

type Banana = {
	type: "fruit";
	color: "yellow";
};

type Tomato = {
	type: "vegetable";
	color: "red";
};

type GroupedByType = GroupBy<Apple | Banana | Tomato, "type">;
//   ^?
// {
//   fruit: Apple | Banana;
//   vegetable: Tomato;
// }

type GroupedByColor = GroupBy<Apple | Banana | Tomato, "color">;
//   ^?
// {
//   green: Apple;
//   yellow: Banana;
//   red: Tomato;
// }

Type Alias GroupBy<T, K>

Type Parameters

Example

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