# -*- coding: utf-8 -*-
from abc import ABC, abstractmethod
from typing import Tuple
[文档]class Dataset(ABC):
r"""An abstract base class for all map-style datasets.
.. admonition:: Abstract methods
All subclasses should overwrite these two methods:
* ``__getitem__()``: fetch a data sample for a given key.
* ``__len__()``: return the size of the dataset.
They play roles in the data pipeline, see the description below.
.. admonition:: Dataset in the Data Pipline
Usually a dataset works with :class:`~.DataLoader`, :class:`~.Sampler`, :class:`~.Collator` and other components.
For example, the sampler generates **indexes** of batches in advance according to the size of the dataset (calling ``__len__``),
When dataloader need to yield a batch of data, pass indexes into the ``__getitem__`` method, then collate them to a batch.
* Highly recommended reading :ref:`dataset-guide` for more details;
* It might helpful to read the implementation of :class:`~.MNIST`, :class:`~.CIFAR10` and other existed subclass.
.. warning::
By default, all elements in a dataset would be :class:`numpy.ndarray`.
It means that if you want to do Tensor operations, it's better to do the conversion explicitly, such as:
.. code-block:: python
dataset = MyCustomDataset() # A subclass of Dataset
data, label = MyCustomDataset[0] # equals to MyCustomDataset.__getitem__[0]
data = Tensor(data, dtype="float32") # convert to MegEngine Tensor explicitly
megengine.functional.ops(data)
Tensor ops on ndarray directly are undefined behaviors.
"""
@abstractmethod
def __init__(self):
pass
@abstractmethod
def __getitem__(self, index):
pass
@abstractmethod
def __len__(self):
pass
[文档]class StreamDataset(Dataset):
r"""An abstract class for stream data.
__iter__ method is aditionally needed.
Examples:
.. code-block:: python
from megengine.data.dataset import StreamDataset
from megengine.data.dataloader import DataLoader, get_worker_info
from megengine.data.sampler import StreamSampler
class MyStream(StreamDataset):
def __init__(self):
self.data = [iter([1, 2, 3]), iter([4, 5, 6]), iter([7, 8, 9])]
def __iter__(self):
worker_info = get_worker_info()
data_iter = self.data[worker_info.idx]
while True:
yield next(data_iter)
dataloader = DataLoader(
dataset = MyStream(),
sampler = StreamSampler(batch_size=2),
num_workers=3,
parallel_stream = True,
)
for step, data in enumerate(dataloader):
print(data)
"""
@abstractmethod
def __init__(self):
pass
@abstractmethod
def __iter__(self):
pass
def __getitem__(self, idx):
raise AssertionError("can not get item from StreamDataset by index")
def __len__(self):
raise AssertionError("StreamDataset does not have length")
[文档]class ArrayDataset(Dataset):
r"""ArrayDataset is a dataset for numpy array data.
One or more numpy arrays are needed to initiate the dataset.
And the dimensions represented sample number are expected to be the same.
Examples:
.. code-block:: python
from megengine.data.dataset import ArrayDataset
from megengine.data.dataloader import DataLoader
from megengine.data.sampler import SequentialSampler
rand_data = np.random.randint(0, 255, size=(sample_num, 1, 32, 32), dtype=np.uint8)
label = np.random.randint(0, 10, size=(sample_num,), dtype=int)
dataset = ArrayDataset(rand_data, label)
seque_sampler = SequentialSampler(dataset, batch_size=2)
dataloader = DataLoader(
dataset,
sampler = seque_sampler,
num_workers=3,
)
for step, data in enumerate(dataloader):
print(data)
"""
def __init__(self, *arrays):
super().__init__()
if not all(len(arrays[0]) == len(array) for array in arrays):
raise ValueError("lengths of input arrays are inconsistent")
self.arrays = arrays
def __getitem__(self, index: int) -> Tuple:
return tuple(array[index] for array in self.arrays)
def __len__(self) -> int:
return len(self.arrays[0])