I’m trying to create a data loader for my NER data as following (Assumption1:  we have two files one for sequences and another one for tag sequences. Assumtion2: Word_to_idx and Tags_to_idx  are ready). Everything seems correct, but dataloader doesn’t work with batch size greater than 1.
class NERdata(Dataset):
    __xs = []
    __ys = []
    def __init__(self,DataFolder,Words_to_idx, Tags_to_idx):
        
        f = open(DataFolder+'/eng.train_seq','r')
        ls = f.readlines()
        f.close()
        f = open(DataFolder+'/eng.train_labels','r')
        ll = f.readlines()
        f.close()
        i = 0
        while(i<len(ll)):
            features = []
            tags = []
            a = ls[i].strip().split()
            b = ll[i].strip().split()
            j = 0
            while(j<len(a)):
                if a[j] in Words_to_idx:
                    features.append(Words_to_idx[a[j].lower()])
                else:
                    features.append(Words_to_idx['UNK'])
                    
                tags.append(Tags_to_idx[b[j]])
                j += 1
            
            
            self.__xs.append(features)
            self.__ys.append(tags)
            i += 1
        
    def __getitem__(self,index):
        Data = self.__xs[index]
        Tags = self.__ys[index]
        return (torch.tensor(Data),torch.tensor(Tags))
    def __len__(self):
        return len(self.__xs)

When I am trying to use dataloader with above defined class like:
dataset = NERdata('data',Words_to_idx,Tags_to_idx)
Data = DataLoader(dataset=dataset,batch_size=2,shuffle=True,num_workers=2)
print(type(Data))
for batch_idx, (data, target) in enumerate(Data):
    print("Data: ", batch_idx, data, target)

I am getting the following runtime error:
RuntimeError: invalid argument 0: Sizes of tensors must match except in dimension 0. Got 30 and 35 in dimension 1 at /pytorch/aten/src/TH/generic/THTensorMoreMath.cpp:1333
any idea about the causes of the problem?