请问在data_loader.py中，__getitem__方法是每个特征单独采样吗？

[ham114]

    def __getitem__(self, index):
        feat_id = index // self.tot_len
        s_begin = index % self.tot_len

        s_end = s_begin + self.seq_len
        r_begin = s_end - self.label_len
        r_end = r_begin + self.label_len + self.pred_len
        seq_x = self.data_x[s_begin:s_end, feat_id:feat_id + 1]
        seq_y = self.data_y[r_begin:r_end, feat_id:feat_id + 1]
        seq_x_mark = self.data_stamp[s_begin:s_end]
        seq_y_mark = self.data_stamp[r_begin:r_end]

        return seq_x, seq_y, seq_x_mark, seq_y_mark
        

这一段没有看懂