Group By

README.md

Group By

Group items by the key returned in the callback.

const data = [
    { id: 'a' },
    { id: 'b' },
    { id: 'a' }
];

groupBy(data, (d) => d.id); // { a: [ { id: 'a' }, { id: 'a' } ], b: [ { id: 'b' } ] }
groupByArray(data, (d) => d.id); // [ { key: 'a', items: [{ id: 'a' }, { id: 'a' }] }, { key: 'b', items: [{ id: 'b' }] } ]

groupBy.js

const groupBy = (items, callback) => {
    const groups = {};

    items.forEach((item) => {
        const key = callback(item) ?? 'ungrouped';
        const keys = Array.isArray(key) ? key : [key];
        
        // Create the group if it doesn't exist.
        keys.forEach((key) => {
            if (!groups[key]) {
                groups[key] = [];
            }

            groups[key].push(item);
        });
    });

    return groups;
};

const groupByArray = (items, callback) => {
    const groups = groupBy(items, callback);

    return Object.keys(groups).map((group) => {
        return {
            key: group,
            items: groups[group]
        };
    });
};