GroupBy an array in TypeScript

groupBy.ts

export interface GroupByModel {
    key: any;
    value: any[];
}

export class Utility {
  static groupBy(xs: any, f: Function): any[] {
    const groupByObjects = xs.reduce((r: any, v: any, i: any, a: any, k = f(v)) => ((r[k] || (r[k] = [])).push(v), r), {});
    const groupByModels: GroupByModel[] = [];
    for (const obj in groupByObjects) {
      if (!groupByObjects.hasOwnProperty(obj)) {
        continue;
      }
      groupByModels.push({
        key: obj,
        value: groupByObjects[obj]
      });
    }
    return groupByModels;
  }
}

// Using:
// Utility.groupBy(arrayToApplyGroupByOnIt, (a) => a.propertyNameToGroupByOnIt)