import numpy as np
from torch.utils.data.dataset import ConcatDataset as _ConcatDataset


class ConcatDataset(_ConcatDataset):
    """A wrapper of concatenated dataset.

    Same as :obj:`torch.utils.data.dataset.ConcatDataset`, but
    concat the group flag for image aspect ratio.

    Args:
        datasets (list[:obj:`Dataset`]): A list of datasets.
    """

    def __init__(self, datasets):
        super(ConcatDataset, self).__init__(datasets)
        self.CLASSES = datasets[0].CLASSES
        if hasattr(datasets[0], 'flag'):
            flags = []
            for i in range(0, len(datasets)):
                flags.append(datasets[i].flag)
            self.flag = np.concatenate(flags)