import torch

class IdentitySubset(torch.utils.data.Dataset):
    def __init__(self, full_ds, indices, id_mapping):
        self.full_ds = full_ds
        self.indices = indices
        self.id_mapping = id_mapping
    def __getitem__(self, idx):
        img, old_id = self.full_ds[self.indices[idx]]
        return img, self.id_mapping[old_id.item()]
    def __len__(self):
        return len(self.indices)