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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sample_batch_trajectories(self, rollout_length):
 """ Return indexes of next random rollout """

        results = []

        for i in range(self.num_envs):
            results.append(self.sample_rollout_single_env(rollout_length))

        return np.stack(results, axis=-1)