Group by multiple values Underscore.JS but keep the keys and values

Question

I\'m trying to group the following array with objects:

[ { user_id: 301, alert_id: 199, deal_id: 32243 },
  { user_id: 301, alert_id: 200, deal_id: 32243 },
         


        

Answer 1

I would like to contribute a neat typescript ES6 group by.
I am not really sure how to tighten up the return value typing. Some trickery is needed there, but this works rather well for me.

/**
 * group the supplied list by a set of keys.
 * @param list the list of items to group.
 * @param children the key for the array of child items.
 * @param components the components to group by.
 */
groupByMultipleFields(
    list: T[],
    children: string,
    ...components: K[]): any[] {

    var grouping = [...list.reduce((r, o) => {
        const key = components.map(_ => `${o[_]}`).join(" :: ");
        var keyed = r.get(key) || components.reduce((x, y) => { x[y] = o[y]; return x; }, {});
        keyed[children] = keyed[children] || [];
        keyed[children].push(o);
        return r.set(key, keyed);
    }, new Map).values()];
    return grouping;

}

You will need to turn on the typescript compiler option "downlevelIteration": true to allow the new Map to iterate and return values().