Basic classes to contain the data for model training.

Get your data ready for training

This module defines the basic DataBunch object that is used inside Learner to train a model. This is the generic class, that can take any kind of fastai Dataset or DataLoader. You'll find helpful functions in the data module of every application to directly create this DataBunch for you.

class DataBunch[source][test]

DataBunch(train_dl:DataLoader, valid_dl:DataLoader, fix_dl:DataLoader=None, test_dl:Optional[DataLoader]=None, device:device=None, dl_tfms:Optional[Collection[Callable]]=None, path:PathOrStr='.', collate_fn:Callable='data_collate', no_check:bool=False)

Tests found for DataBunch:

  • pytest -sv tests/test_data_block.py::test_custom_dataset [source]

Some other tests where DataBunch is used:

  • pytest -sv tests/test_basic_data.py::test_DataBunch_Create [source]
  • pytest -sv tests/test_basic_data.py::test_DataBunch_no_valid_dl [source]
  • pytest -sv tests/test_basic_data.py::test_DataBunch_save_load [source]

To run tests please refer to this guide.

Bind train_dl,valid_dl and test_dl in a data object.

It also ensures all the dataloaders are on device and applies to them dl_tfms as batch are drawn (like normalization). path is used internally to store temporary files, collate_fn is passed to the pytorch Dataloader (replacing the one there) to explain how to collate the samples picked for a batch. By default, it applies data to the object sent (see in vision.image or the data block API why this can be important).

train_dl, valid_dl and optionally test_dl will be wrapped in DeviceDataLoader.

Factory method

create[source][test]

create(train_ds:Dataset, valid_ds:Dataset, test_ds:Optional[Dataset]=None, path:PathOrStr='.', bs:int=64, val_bs:int=None, num_workers:int=8, dl_tfms:Optional[Collection[Callable]]=None, device:device=None, collate_fn:Callable='data_collate', no_check:bool=False, **dl_kwargs) → DataBunch

Tests found for create:

  • pytest -sv tests/test_basic_data.py::test_DataBunch_Create [source]
  • pytest -sv tests/test_basic_data.py::test_DataBunch_no_valid_dl [source]

Some other tests where create is used:

  • pytest -sv tests/test_basic_data.py::test_DeviceDataLoader_getitem [source]

To run tests please refer to this guide.

Create a DataBunch from train_ds, valid_ds and maybe test_ds with a batch size of bs. Passes **dl_kwargs to DataLoader()

num_workers is the number of CPUs to use, tfms, device and collate_fn are passed to the init method.

Visualization

show_batch[source][test]

show_batch(rows:int=5, ds_type:DatasetType=<DatasetType.Train: 1>, reverse:bool=False, **kwargs)

Tests found for show_batch:

  • pytest -sv tests/test_basic_data.py::test_DataBunch_show_batch [source]

To run tests please refer to this guide.

Show a batch of data in ds_type on a few rows.

Grabbing some data

dl[source][test]

dl(ds_type:DatasetType=<DatasetType.Valid: 2>) → DeviceDataLoader

No tests found for dl. To contribute a test please refer to this guide and this discussion.

Returns an appropriate DataLoader with a dataset for validation, training, or test (ds_type).

one_batch[source][test]

one_batch(ds_type:DatasetType=<DatasetType.Train: 1>, detach:bool=True, denorm:bool=True, cpu:bool=True) → Collection[Tensor]

Tests found for one_batch:

  • pytest -sv tests/test_basic_data.py::test_DataBunch_onebatch [source]
  • pytest -sv tests/test_basic_data.py::test_DataBunch_save_load [source]
  • pytest -sv tests/test_text_data.py::test_backwards_cls_databunch [source]
  • pytest -sv tests/test_text_data.py::test_should_load_backwards_lm_1 [source]
  • pytest -sv tests/test_text_data.py::test_should_load_backwards_lm_2 [source]

To run tests please refer to this guide.

Get one batch from the data loader of ds_type. Optionally detach and denorm.

one_item[source][test]

one_item(item, detach:bool=False, denorm:bool=False, cpu:bool=False)

Tests found for one_item:

  • pytest -sv tests/test_basic_data.py::test_DataBunch_oneitem [source]

To run tests please refer to this guide.

Get item into a batch. Optionally detach and denorm.

sanity_check[source][test]

sanity_check()

No tests found for sanity_check. To contribute a test please refer to this guide and this discussion.

Check the underlying data in the training set can be properly loaded.

Load and save

You can save your DataBunch object for future use with this method.

save[source][test]

save(file:PathLikeOrBinaryStream='data_save.pkl')

Tests found for save:

  • pytest -sv tests/test_basic_data.py::test_DataBunch_save_load [source]

To run tests please refer to this guide.

Save the DataBunch in self.path/file. file can be file-like (file or buffer)

load_data[source][test]

load_data(path:PathOrStr, file:PathLikeOrBinaryStream='data_save.pkl', bs:int=64, val_bs:int=None, num_workers:int=8, dl_tfms:Optional[Collection[Callable]]=None, device:device=None, collate_fn:Callable='data_collate', no_check:bool=False, **kwargs) → DataBunch

Tests found for load_data:

  • pytest -sv tests/test_basic_data.py::test_DataBunch_save_load [source]
  • pytest -sv tests/test_text_data.py::test_load_and_save_test [source]

To run tests please refer to this guide.

Load a saved DataBunch from path/file. file can be file-like (file or buffer)

This is to allow you to easily create a new DataBunch with a different batch size for instance. You will also need to reapply any normalization (in vision) you might have done on your original DataBunch.

Empty DataBunch for inference

export[source][test]

export(file:PathLikeOrBinaryStream='export.pkl')

No tests found for export. To contribute a test please refer to this guide and this discussion.

Export the minimal state of self for inference in self.path/file. file can be file-like (file or buffer)

load_empty[source][test]

load_empty(path, fname:str='export.pkl')

No tests found for _databunch_load_empty. To contribute a test please refer to this guide and this discussion.

Load an empty DataBunch from the exported file in path/fname with optional tfms.

This method should be used to create a DataBunch at inference, see the corresponding tutorial.

add_test[source][test]

add_test(items:Iterator[T_co], label:Any=None, tfms=None, tfm_y=None)

No tests found for add_test. To contribute a test please refer to this guide and this discussion.

Add the items as a test set. Pass along label otherwise label them with EmptyLabel.

Dataloader transforms

add_tfm[source][test]

add_tfm(tfm:Callable)

No tests found for add_tfm. To contribute a test please refer to this guide and this discussion.

Adds a transform to all dataloaders.

Using a custom Dataset in fastai

If you want to use your pytorch Dataset in fastai, you may need to implement more attributes/methods if you want to use the full functionality of the library. Some functions can easily be used with your pytorch Dataset if you just add an attribute, for others, the best would be to create your own ItemList by following this tutorial. Here is a full list of what the library will expect.

Basics

First of all, you obviously need to implement the methods __len__ and __getitem__, as indicated by the pytorch docs. Then the most needed things would be:

Toy example with image-like numpy arrays and binary label

class ArrayDataset(Dataset):
    "Sample numpy array dataset"
    def __init__(self, x, y):
        self.x, self.y = x, y
        self.c = 2 # binary label
    
    def __len__(self):
        return len(self.x)
    
    def __getitem__(self, i):
        return self.x[i], self.y[i]

train_x = np.random.rand(10, 3, 3) # 10 images (3x3)
train_y = np.random.rand(10, 1).round() # binary label

valid_x = np.random.rand(10, 3, 3)
valid_y = np.random.rand(10, 1).round()

train_ds, valid_ds = ArrayDataset(train_x, train_y), ArrayDataset(valid_x, valid_y)
data = DataBunch.create(train_ds, valid_ds, bs=2, num_workers=1)
data.one_batch()

(tensor([[[0.8053, 0.5914, 0.5369],
          [0.6880, 0.4680, 0.5457],
          [0.0051, 0.2096, 0.3469]],
 
         [[0.5170, 0.2542, 0.9869],
          [0.0176, 0.5049, 0.4417],
          [0.3495, 0.7276, 0.5426]]], dtype=torch.float64), tensor([[0.],
         [0.]], dtype=torch.float64))

For a specific application

In text, your dataset will need to have a vocab attribute that should be an instance of Vocab. It's used by text_classifier_learner and language_model_learner when building the model.

In tabular, your dataset will need to have a cont_names attribute (for the names of continuous variables) and a get_emb_szs method that returns a list of tuple (n_classes, emb_sz) representing, for each categorical variable, the number of different codes (don't forget to add 1 for nan) and the corresponding embedding size. Those two are used with the c attribute by tabular_learner.

Functions that really won't work

To make those last functions work, you really need to use the data block API and maybe write your own custom ItemList.

class DeviceDataLoader[source][test]

DeviceDataLoader(dl:DataLoader, device:device, tfms:List[Callable]=None, collate_fn:Callable='data_collate')

Tests found for DeviceDataLoader:

Some other tests where DeviceDataLoader is used:

  • pytest -sv tests/test_basic_data.py::test_DeviceDataLoader_getitem [source]

To run tests please refer to this guide.

Bind a DataLoader to a torch.device.

Put the batches of dl on device after applying an optional list of tfms. collate_fn will replace the one of dl. All dataloaders of a DataBunch are of this type.

Factory method

create[source][test]

create(dataset:Dataset, bs:int=64, shuffle:bool=False, device:device=device(type='cpu'), tfms:Collection[Callable]=None, num_workers:int=8, collate_fn:Callable='data_collate', **kwargs:Any)

Tests found for create:

Some other tests where create is used:

  • pytest -sv tests/test_basic_data.py::test_DataBunch_Create [source]
  • pytest -sv tests/test_basic_data.py::test_DataBunch_no_valid_dl [source]
  • pytest -sv tests/test_basic_data.py::test_DeviceDataLoader_getitem [source]

To run tests please refer to this guide.

Create DeviceDataLoader from dataset with bs and shuffle: process using num_workers.

The given collate_fn will be used to put the samples together in one batch (by default it grabs their data attribute). shuffle means the dataloader will take the samples randomly if that flag is set to True, or in the right order otherwise. tfms are passed to the init method. All kwargs are passed to the pytorch DataLoader class initialization.

Methods

add_tfm[source][test]

add_tfm(tfm:Callable)

No tests found for add_tfm. To contribute a test please refer to this guide and this discussion.

Add tfm to self.tfms.

remove_tfm[source][test]

remove_tfm(tfm:Callable)

No tests found for remove_tfm. To contribute a test please refer to this guide and this discussion.

Remove tfm from self.tfms.

new[source][test]

new(**kwargs)

No tests found for new. To contribute a test please refer to this guide and this discussion.

Create a new copy of self with kwargs replacing current values.

proc_batch[source][test]

proc_batch(b:Tensor) → Tensor

No tests found for proc_batch. To contribute a test please refer to this guide and this discussion.

Process batch b of TensorImage.

`DatasetType`[test]

Enum = [Train, Valid, Test, Single, Fix]

No tests found for DatasetType. To contribute a test please refer to this guide and this discussion.

Internal enumerator to name the training, validation and test dataset/dataloader.

Open This Notebook