groupBy.ts

/**
 * Group array of objects by given keys
 *
 * @param keys keys to be grouped by
 * @param array objects to be grouped
 *
 * @returns an object with objects in `array` grouped by `keys`
 */
export const groupBy = <T>(keys: (keyof T)[]) => (array: T[]): Record<string, T[]> => {
    return array.reduce((objectsByKeyValue, obj) => {
        const value = keys.map((key) => obj[key]).join('-');
        objectsByKeyValue[value] = (objectsByKeyValue[value] || []).concat(obj);

        return objectsByKeyValue;
    }, {} as Record<string, T[]>);
}