array of objects to object of arrays

arrayify.ts

type ArrayifyFields<Original> = Original extends Record<string, unknown>
	? {
			[key in keyof Original]: Original[key][]
	  }
	: never

export function arrayifyFields<Item extends Record<string, unknown>>(items: Item[]) {
	return items.reduce((grouped, item) => {
		const entries = Object.entries(item).map(
			([key, value]) => [key, grouped ? [grouped[key], value] : [value]] as const,
		)
		return Object.fromEntries(entries) as ArrayifyFields<Item>
	}, null as null | ArrayifyFields<Item>)
}

export function groupByName<Item extends { name: string }>(items: Item[]): Item[][] {
	const repo: Record<string, Item[]> = {}

	items.forEach(item => {
		repo[item.name] = [...(repo[item.name] ?? []), item]
	})

	return Object.entries(repo).map(([_key, value]) => value)
}