code: public function randomKeys($size)
      {
          Assert::notEmpty($this->items, 'Cannot retrieve a random key/value for empty bags.');
          Assert::range($size, 1, $this->count(), 'Expected $size to be between 1 and %3$s (the number of items in the bag). Got: %s');
  
          return $this->createFrom((array) array_rand($this->items, $size));
      }
docs: Returns a list with a random number of keys (as values).
  
  @param int $size Number of keys
  
  @throws \InvalidArgumentException when the bag is empty or the given $size is greater than the number of items
  
  @return static