Count

Count the number of items in the given list

🎬 Usage

<script>
    import {count} from "@sveu/shared/lists"

    let list = [
        {id: 1, name: "John"},
        {id: 2, name: "Jane"},
        {id: 3, name: "John"},
        {id: 4, name: "John"},
        {id: 5, name: "Jane"},
    ]

    const counts = count(list, item => item.name) // {John: 3, Jane: 2}

    const actors = ["Mila", "John", "Jane", "John", "John", "Mila", "Mila"]


    const counts2 = count(actors, actor => actor) // {Mila: 3, John: 3, Jane: 1}
</script>

👩‍💻API

👻 Arguments

Name	Description	Type	Required
list	The list to count	`T[]`	Yes
fn	A function that returns the id of an item or the field to count.	`(item: T) => string \| number \| symbol`	Yes

↩️ Returns

A key-value pair of the number of times each item appears.

🧪 Playground

Source Code 👀

Source Code

import type { Dict } from "../../utils"

/**
 * Counts the number of times each item appears in a list.
 *
 * @param list -  The list to count.
 *
 * @param fn -  A function that returns the id of an item or the field to count.
 *
 * @returns A record of the number of times each item appears in the list.
 */
export function count<T extends Dict>(
    list: T[],
    fn: (item: T) => string | number | symbol
) {
    return list.reduce((acc, item) => {
        const id = fn(item)
        return {
            ...acc,
            [id]: (acc[id] ?? 0) + 1,
        }
    }, {} as Record<string | number | symbol, number>)
}

Last update: 2023-02-14

Authors: Mohamed-Kaizen