Batch size keeps on changin, throwing `Pytorch Value Error Expected: input batch size does not match target batch size`

I am working on a multilabel text classification task with Bert.

The following is the code for generating an iterable Dataset.

from import TensorDataset, DataLoader, RandomSampler, SequentialSampler

train_set = TensorDataset(X_train_id,X_train_attention, y_train)
test_set = TensorDataset(X_test_id,X_test_attention,y_test)

train_dataloader = DataLoader(
    sampler = RandomSampler(train_set),

test_dataloader = DataLoader(
    sampler = SequentialSampler(test_set),

The following are the the dimensions of the training set:




torch.Size([262754, 512])
torch.Size([262754, 512])
torch.Size([262754, 34])

There should be 262754 rows each with 512 columns. The output should predict the values from 34 possible labels. I am breaking them down into batches of 13.

Training code

optimizer = AdamW(model.parameters(), lr=2e-5)
# Training
def train(model):
    train_loss = 0
    for batch in train_dataloader:
        b_input_ids = batch[0].to(device)
        b_input_mask = batch[1].to(device)
        b_labels = batch[2].to(device)
        loss, logits = model(b_input_ids, 
        torch.nn.utils.clip_grad_norm_(model.parameters(), 1.0)
        train_loss += loss.item()
    return train_loss

# Testing
def test(model):
    val_loss = 0
    with torch.no_grad():
        for batch in test_dataloader:
            b_input_ids = batch[0].to(device)
            b_input_mask = batch[1].to(device)
            b_labels = batch[2].to(device)
            with torch.no_grad():        
                (loss, logits) = model(b_input_ids, 
            val_loss += loss.item()
    return val_loss

# Train task
max_epoch = 1
train_loss_ = []
test_loss_ = []

for epoch in range(max_epoch):
    train_ = train(model)
    test_ = test(model)


Expected input batch_size (13) to match target batch_size (442).

This is the description of my model:

from transformers import BertForSequenceClassification, AdamW, BertConfig

model = BertForSequenceClassification.from_pretrained(
    "cl-tohoku/bert-base-japanese-whole-word-masking", # 日本語Pre trainedモデル
    num_labels = 34, 
    output_attentions = False,
    output_hidden_states = False,

I have clearly stated that I want the batch size to be 13. However, during the training process pytorch is throwing a Runtime Error

Where is the number 442 even coming from? I have clearly stated that I want each batch to have a size of 13 rows.

I have already confirmed that each batch has input_id with dimensions [13,512], attention tensor with dimensions [13,512], and labels with dimensions [13,34].

I have tried caving in and using a batch size of 442 when initializing the DataLoader, but after a single batch iteration, it throws another Pytorch Value Error Expected: input batch size does not match target batch size, this time showing:

ValueError: Expected input batch_size (442) to match target batch_size (15028).

Why does the batch size keep on changing? Where is the number 15028 even coming from?

The following are some of the answers I have looked through, but had no luck on applying to my source code because none of them talk about batch sizes changing:

Thanks in advance. Your support is truly appreciated :slight_smile:

I think it’s the flattened target tensor: [13*43=442].
Based on the docs for BertForSequenceClassification, the targets are expected as [batch_size] so they are most likely internally flattened.

I’m not familiar with the implementation, but since it’s a classification use case I guess the targets have the same (or similar) requirements as the targets for nn.CrossEntropyLoss.
I.e. they are expected in the shape [batch_size] as LongTensors containing the class indices in the range [0, nb_classes-1] for a multi-class classification use case.

Thanks for the feedback.

However, I have confirmed that during each iteration during the training, my dimensions are:

input_ids: [13,512]
input_masks: [13,512]
y_labels: [13,34]

where 34 is the number of possible labels (as one hot vectors).
[0,0,0,1,1,0,0,… 0,1]

Doesn’t this meet the requirement for calculating Cross EntropyLoss ?

Screen Shot 2020-10-06 at 10.32.50

No, since class labels are expected.
Use target = torch.argmax(target, dim=1) to create the expected target tensor.

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