fairnesscoop / permacoop

  public static range(start: number, end: number, step = 1) {

    function* generateRange() {

      let x = start - step;

      while (x <= end - step) {

        yield (x += step);

      }

    }

    return {

      [Symbol.iterator]: generateRange

    };

  }

  public static groupBy<T>(

    xs: Array<T>,

    key: (x: T) => string

  ): { [key: string]: T } {

    // Credit: https://stackoverflow.com/a/34890276

    return xs.reduce(function(rv, x) {

      (rv[key(x)] = rv[key(x)] || []).push(x);

      return rv;

    }, {});

  }

}