Can’t train a multilabel classifier on a small dataset
I have a dataset of 3 classes animals, landscapes, and buildings. It is only a 100 images per dataset and I am trying to train a classifier using ResNet34 + fastai but I'm running into several issues.
The first one is that I don't think my model is training properly. When I use the lr_finder, my validation loss is na, unless this is expected:

Then I run 10 epochs. It looks either like its learning well or its overfitting like hell.

Then I unfreeze to find another learning rate and my validation loss is still na:

And now when I train 10 epochs, the graph starts to oscillate so that tells me that it can't learn anymore. The accuracy looks good (unless its overfitting) so then I decide to use my validation set to see how my model is actually doing:

Because I have 300 images, 240 are in the train folder and 60 are in the test folder. My test images are labelled because I want to run an accuracy score on it. This is the cell that I run:
    path = '/content/dataset/'

    data_test = ImageList.from_folder(path).split_by_folder(train='train', valid='test').label_from_re(file_parse).transform(size=512).databunch().normalize(imagenet_stats)

    learn = cnn_learner(data, models.resnet50, metrics=[accuracy, top_1],callback_fns=ShowGraph)

    learn.load('stage-2')

And this is the error that I am met with:
    RuntimeError                              Traceback (most recent call last)
    &lt;ipython-input-28-f1232eb8cf47&gt; in &lt;module&gt;()
      4 
      5 learn = cnn_learner(data, models.resnet50, metrics=[accuracy, top_1],callback_fns=ShowGraph)
    ----&gt; 6 learn.load('stage-2')

    1 frames
    /usr/local/lib/python3.7/dist-packages/torch/nn/modules/module.py in load_state_dict(self, state_dict, strict)
    828         if len(error_msgs) &gt; 0:
    829             raise RuntimeError('Error(s) in loading state_dict for {}:\n\t{}'.format(
    --&gt; 830                                self.__class__.__name__, &quot;\n\t&quot;.join(error_msgs)))
    831         return _IncompatibleKeys(missing_keys, unexpected_keys)
    832 

    RuntimeError: Error(s) in loading state_dict for Sequential:
        Missing key(s) in state_dict: &quot;0.4.0.conv3.weight&quot;, &quot;0.4.0.bn3.weight&quot;, &quot;0.4.0.bn3.bias&quot;, &quot;0.4.0.bn3.running_mean&quot;, &quot;0.4.0.bn3.running_var&quot;, &quot;0.4.0.downsample.0.weight&quot;, &quot;0.4.0.downsample.1.weight&quot;, &quot;0.4.0.downsample.1.bias&quot;, &quot;0.4.0.downsample.1.running_mean&quot;, &quot;0.4.0.downsample.1.running_var&quot;, &quot;0.4.1.conv3.weight&quot;, &quot;0.4.1.bn3.weight&quot;, &quot;0.4.1.bn3.bias&quot;, &quot;0.4.1.bn3.running_mean&quot;, &quot;0.4.1.bn3.running_var&quot;, &quot;0.4.2.conv3.weight&quot;, &quot;0.4.2.bn3.weight&quot;, &quot;0.4.2.bn3.bias&quot;, &quot;0.4.2.bn3.running_mean&quot;, &quot;0.4.2.bn3.running_var&quot;, &quot;0.5.0.conv3.weight&quot;, &quot;0.5.0.bn3.weight&quot;, &quot;0.5.0.bn3.bias&quot;, &quot;0.5.0.bn3.running_mean&quot;, &quot;0.5.0.bn3.running_var&quot;, &quot;0.5.1.conv3.weight&quot;, &quot;0.5.1.bn3.weight&quot;, &quot;0.5.1.bn3.bias&quot;, &quot;0.5.1.bn3.running_mean&quot;, &quot;0.5.1.bn3.running_var&quot;, &quot;0.5.2.conv3.weight&quot;, &quot;0.5.2.bn3.weight&quot;, &quot;0.5.2.bn3.bias&quot;, &quot;0.5.2.bn3.running_mean&quot;, &quot;0.5.2.bn3.running_var&quot;, &quot;0.5.3.conv3.weight&quot;, &quot;0.5.3.bn3.weight&quot;, &quot;0.5.3.bn3.bias&quot;, &quot;0.5.3.bn3.running_mean&quot;, &quot;0.5.3.bn3.running_var&quot;, &quot;0.6.0.conv3.weight&quot;, &quot;0.6.0.bn3.weight&quot;, &quot;0.6.0.bn3.bias&quot;, &quot;0.6.0.bn3.running_mean&quot;, &quot;0.6.0.bn3.running_var&quot;, &quot;0.6.1.conv3.weight&quot;, &quot;0.6.1.bn3.weight&quot;, &quot;0.6.1.bn3.bias&quot;, &quot;0.6.1.bn3.running_mean&quot;, &quot;0.6.1.bn3.running_var&quot;, &quot;0.6.2.conv3.weight&quot;, &quot;0.6.2.bn3.weight&quot;, &quot;0.6.2.bn3.bias&quot;, &quot;0.6.2.bn3.running_mean&quot;, &quot;0.6.2.bn3.running_var&quot;, &quot;0.6.3.conv3.weight&quot;, &quot;0.6.3.bn3.weight&quot;, &quot;0.6.3.bn3.bias&quot;, &quot;0.6.3.bn3.running_mean&quot;, &quot;0.6.3.bn3.running_var&quot;, &quot;0.6.4.conv3.weight&quot;, &quot;0.6.4.bn3.weight&quot;, &quot;0.6.4.bn3.bias&quot;, &quot;0.6.4.bn3.running_mean&quot;, &quot;0.6....
        size mismatch for 0.4.0.conv1.weight: copying a param with shape torch.Size([64, 64, 3, 3]) from checkpoint, the shape in current model is torch.Size([64, 64, 1, 1]).
        size mismatch for 0.4.1.conv1.weight: copying a param with shape torch.Size([64, 64, 3, 3]) from checkpoint, the shape in current model is torch.Size([64, 256, 1, 1]).
        size mismatch for 0.4.2.conv1.weight: copying a param with shape torch.Size([64, 64, 3, 3]) from checkpoint, the shape in current model is torch.Size([64, 256, 1, 1]).
        size mismatch for 0.5.0.conv1.weight: copying a param with shape torch.Size([128, 64, 3, 3]) from checkpoint, the shape in current model is torch.Size([128, 256, 1, 1]).
        size mismatch for 0.5.0.downsample.0.weight: copying a param with shape torch.Size([128, 64, 1, 1]) from checkpoint, the shape in current model is torch.Size([512, 256, 1, 1]).
        size mismatch for 0.5.0.downsample.1.weight: copying a param with shape torch.Size([128]) from checkpoint, the shape in current model is torch.Size([512]).
        size mismatch for 0.5.0.downsample.1.bias: copying a param with shape torch.Size([128]) from checkpoint, the shape in current model is torch.Size([512]).
        size mismatch for 0.5.0.downsample.1.running_mean: copying a param with shape torch.Size([128]) from checkpoint, the shape in current model is torch.Size([512]).
        size mismatch for 0.5.0.downsample.1.running_var: copying a param with shape torch.Size([128]) from checkpoint, the shape in current model is torch.Size([512]).
        size mismatch for 0.5.1.conv1.weight: copying a param with shape torch.Size([128, 128, 3, 3]) from checkpoint, the shape in current model is torch.Size([128, 512, 1, 1]).
        size mismatch for 0.5.2.conv1.weight: copying a param with shape torch.Size([128, 128, 3, 3]) from checkpoint, the shape in current model is torch.Size([128, 512, 1, 1]).
        size mismatch for 0.5.3.conv1.weight: copying a param with shape torch.Size([128, 128, 3, 3]) from checkpoint, the shape in current model is torch.Size([128, 512, 1, 1]).
        size mismatch for 0.6.0.conv1.weight: copying a param with shape torch.Size([256, 128, 3, 3]) from checkpoint, the shape in current model is torch.Size([256, 512, 1, 1]).
        size mismatch for 0.6.0.downsample.0.weight: copying a param with shape torch.Size([256, 128, 1, 1]) from checkpoint, the shape in current model is torch.Size([1024, 512, 1, 1]).
        size mismatch for 0.6.0.downsample.1.weight: copying a param with shape torch.Size([256]) from checkpoint, the shape in current model is torch.Size([1024]).
        size mismatch for 0.6.0.downsample.1.bias: copying a param with shape torch.Size([256]) from checkpoint, the shape in current model is torch.Size([1024]).
        size mismatch for 0.6.0.downsample.1.running_mean: copying a param with shape torch.Size([256]) from checkpoint, the shape in current model is torch.Size([1024]).
        size mismatch for 0.6.0.downsample.1.running_var: copying a param with shape torch.Size([256]) from checkpoint, the shape in current model is torch.Size([1024]).
        size mismatch for 0.6.1.conv1.weight: copying a param with shape torch.Size([256, 256, 3, 3]) from checkpoint, the shape in current model is torch.Size([256, 1024, 1, 1]).
        size mismatch for 0.6.2.conv1.weight: copying a param with shape torch.Size([256, 256, 3, 3]) from checkpoint, the shape in current model is torch.Size([256, 1024, 1, 1]).
        size mismatch for 0.6.3.conv1.weight: copying a param with shape torch.Size([256, 256, 3, 3]) from checkpoint, the shape in current model is torch.Size([256, 1024, 1, 1]).
        size mismatch for 0.6.4.conv1.weight: copying a param with shape torch.Size([256, 256, 3, 3]) from checkpoint, the shape in current model is torch.Size([256, 1024, 1, 1]).
        size mismatch for 0.6.5.conv1.weight: copying a param with shape torch.Size([256, 256, 3, 3]) from checkpoint, the shape in current model is torch.Size([256, 1024, 1, 1]).
        size mismatch for 0.7.0.conv1.weight: copying a param with shape torch.Size([512, 256, 3, 3]) from checkpoint, the shape in current model is torch.Size([512, 1024, 1, 1]).
        size mismatch for 0.7.0.downsample.0.weight: copying a param with shape torch.Size([512, 256, 1, 1]) from checkpoint, the shape in current model is torch.Size([2048, 1024, 1, 1]).
        size mismatch for 0.7.0.downsample.1.weight: copying a param with shape torch.Size([512]) from checkpoint, the shape in current model is torch.Size([2048]).
        size mismatch for 0.7.0.downsample.1.bias: copying a param with shape torch.Size([512]) from checkpoint, the shape in current model is torch.Size([2048]).
        size mismatch for 0.7.0.downsample.1.running_mean: copying a param with shape torch.Size([512]) from checkpoint, the shape in current model is torch.Size([2048]).
        size mismatch for 0.7.0.downsample.1.running_var: copying a param with shape torch.Size([512]) from checkpoint, the shape in current model is torch.Size([2048]).
        size mismatch for 0.7.1.conv1.weight: copying a param with shape torch.Size([512, 512, 3, 3]) from checkpoint, the shape in current model is torch.Size([512, 2048, 1, 1]).
        size mismatch for 0.7.2.conv1.weight: copying a param with shape torch.Size([512, 512, 3, 3]) from checkpoint, the shape in current model is torch.Size([512, 2048, 1, 1]).
        size mismatch for 1.2.weight: copying a param with shape torch.Size([1024]) from checkpoint, the shape in current model is torch.Size([4096]).
        size mismatch for 1.2.bias: copying a param with shape torch.Size([1024]) from checkpoint, the shape in current model is torch.Size([4096]).
        size mismatch for 1.2.running_mean: copying a param with shape torch.Size([1024]) from checkpoint, the shape in current model is torch.Size([4096]).
        size mismatch for 1.2.running_var: copying a param with shape torch.Size([1024]) from checkpoint, the shape in current model is torch.Size([4096]).
        size mismatch for 1.4.weight: copying a param with shape torch.Size([512, 1024]) from checkpoint, the shape in current model is torch.Size([512, 4096]).


There are few issues with your approach  :

You mentioned that you used resnet 34 for training and then saving its weights. Yet while testing, you are using resnet 50 and trying to load the weights of resnet 34 which will not work due to different arch (layers &amp; parameters).

In case  you are doing the testing in the same NB , you cold have added test dataset  while creating the train &amp; valid dataset itself and get predictions on the whole dataset with 2 lines of code. a quick sample :
test_imgs = (path/'cars_test/').ls()
data.add_test(test_imgs)
learn.data = data
preds = learn.get_preds(ds_type=DatasetType.Test)

If you are going to use it in different nb , try model.export to save model, its weights, data and all the info . I think jeremy did that in his NB and course.


