group

The group() function groups iterable elements into an object of arrays using a group name returned by your callback.

Interactive example

Syntax

Classic signature

function group<
	GenericElement extends unknown,
	GenericOutput extends GroupFunctionOutput,
>(
	iterator: Iterable<GenericElement>,
	theFunction: (
		element: GenericElement,
		params: GroupFunctionParams
	) => GenericOutput,
): GroupResult<GenericOutput>

Curried signature

function group<
	GenericElement extends unknown,
	GenericOutput extends GroupFunctionOutput,
>(
	theFunction: (
		element: GenericElement,
		params: GroupFunctionParams
	) => GenericOutput,
): (iterator: Iterable<GenericElement>) => GroupResult<GenericOutput>

Parameters

• iterator: The iterable source to group.
• theFunction: Grouping function that receives:
• element: The current element.
• params.index: The current index.
• params.output(group, value): Helper to build a typed group output.

Return value

An object where each key is a group name and each value is an array of grouped values. Keys are optional because a group can be absent in the final result.

See also

• asyncGroup - Asynchronous version of group
• reduce - Reduces a generator to a single value