Add random_split and Subset dataset (#29291)

As the title 

python/paddle/fluid/dataloader/dataset.py

@@ -19,7 +19,7 @@ import paddle.dataset.common
 
 __all__ = [
     "Dataset", "IterableDataset", "TensorDataset", "ComposeDataset",
-    "ChainDataset"
+    "ChainDataset", "random_split", "Subset"
 ]
 
 
@@ -400,3 +400,131 @@ class ChainDataset(IterableDataset):
         for dataset in self.datasets:
             for sample in dataset:
                 yield sample
+
+
+class Subset(Dataset):
+    """
+    Subset of a dataset at specified indices.
+    
+    Args:
+        dataset (Dataset): The whole Dataset.
+        indices (sequence): Indices in the whole set selected for subset.
+
+    Returns:
+        Dataset: A Dataset which is the subset of the original dataset.
+    
+    Example code:
+
+        .. code-block:: python
+
+            import paddle
+            from paddle.io import Subset
+
+            # example 1:
+            a = paddle.io.Subset(dataset=range(1, 4), indices=[0, 2])
+            print(list(a))
+            # [1, 3]
+
+            # example 2:
+            b = paddle.io.Subset(dataset=range(1, 4), indices=[1, 1])
+            print(list(b))
+            # [2, 2]
+    """
+
+    def __init__(self, dataset, indices):
+        self.dataset = dataset
+        self.indices = indices
+
+    def __getitem__(self, idx):
+        return self.dataset[self.indices[idx]]
+
+    def __len__(self):
+        return len(self.indices)
+
+
+def random_split(dataset, lengths, generator=None):
+    """
+    Randomly split a dataset into non-overlapping new datasets of given lengths.
+    Optionally fix the generator for reproducible results, e.g.:
+
+    Args:
+        dataset (Dataset): Dataset to be split
+        lengths (sequence): lengths of splits to be produced
+        generator (Generator, optional): Generator used for the random permutation. Default is None then the DefaultGenerator is used in manual_seed().
+
+     Returns:
+        Datasets: A list of subset Datasets, which are the non-overlapping subsets of the original Dataset.
+
+    Example code:
+
+        .. code-block:: python
+
+            import paddle
+            from paddle.io import random_split
+
+            a_list = paddle.io.random_split(range(10), [3, 7])
+            print(len(a_list)) 
+            # 2
+
+            for idx, v in enumerate(a_list[0]):
+                print(idx, v)
+
+            # output of the first subset
+            # 0 1
+            # 1 3
+            # 2 9
+
+            for idx, v in enumerate(a_list[1]):
+                print(idx, v)
+            # output of the second subset
+            # 0 5
+            # 1 7
+            # 2 8
+            # 3 6
+            # 4 0
+            # 5 2
+            # 6 4
+    """
+    # Cannot verify that dataset is Sized
+    if sum(lengths) != len(dataset):  # type: ignore
+        raise ValueError(
+            "Sum of input lengths does not equal the length of the input dataset!"
+        )
+    # TODO(@Joejiong): support Variable or Tensor type with .tolist class member function.
+    # For example var.item() and var.tolist()
+    indices = paddle.randperm(sum(lengths)).numpy().tolist()
+    return [
+        Subset(dataset, indices[offset - length:offset])
+        for offset, length in zip(_accumulate(lengths), lengths)
+    ]
+
+
+def _accumulate(iterable, fn=lambda x, y: x + y):
+    """
+    Return running totals
+    
+    Args:
+        iterable: any iterable object for example dataset.
+        y (x): one element in the iterable object.
+        fn (x, y): Defaults to lambdax.
+
+    Yields:
+        yields total from beginning iterator to current iterator.
+
+    Example code:
+    
+        .. code-block:: python
+        
+            _accumulate([1,2,3,4,5]) --> 1 3 6 10 15
+            _accumulate([1,2,3,4,5], operator.mul) --> 1 2 6 24 120
+    """
+
+    it = iter(iterable)
+    try:
+        total = next(it)
+    except StopIteration:
+        return
+    yield total
+    for element in it:
+        total = fn(total, element)
+        yield total

python/paddle/fluid/tests/unittests/test_multiprocess_dataloader_dataset.py

@@ -20,8 +20,7 @@ import numpy as np
 import paddle
 import paddle.fluid as fluid
 from paddle.io import Dataset, IterableDataset, TensorDataset, \
-        ComposeDataset, ChainDataset, DataLoader
-from paddle.fluid.dygraph.base import to_variable
+        ComposeDataset, ChainDataset, DataLoader, random_split, Subset
 
 IMAGE_SIZE = 32
 
@@ -54,14 +53,14 @@ class RandomIterableDataset(IterableDataset):
 
 class TestTensorDataset(unittest.TestCase):
     def run_main(self, num_workers, places):
-        fluid.default_startup_program().random_seed = 1
-        fluid.default_main_program().random_seed = 1
-        place = fluid.CPUPlace()
+        paddle.static.default_startup_program().random_seed = 1
+        paddle.static.default_main_program().random_seed = 1
+        place = paddle.CPUPlace()
         with fluid.dygraph.guard(place):
             input_np = np.random.random([16, 3, 4]).astype('float32')
-            input = to_variable(input_np)
+            input = paddle.to_tensor(input_np)
             label_np = np.random.random([16, 1]).astype('int32')
-            label = to_variable(label_np)
+            label = paddle.to_tensor(label_np)
 
             dataset = TensorDataset([input, label])
             assert len(dataset) == 16
@@ -83,17 +82,17 @@ class TestTensorDataset(unittest.TestCase):
                 assert np.allclose(label.numpy(), label_np[i])
 
     def test_main(self):
-        places = [fluid.CPUPlace()]
-        if fluid.core.is_compiled_with_cuda():
-            places.append(fluid.CUDAPlace(0))
+        places = [paddle.CPUPlace()]
+        if paddle.is_compiled_with_cuda():
+            places.append(paddle.CUDAPlace(0))
         for p in places:
             self.run_main(num_workers=0, places=p)
 
 
 class TestComposeDataset(unittest.TestCase):
     def test_main(self):
-        fluid.default_startup_program().random_seed = 1
-        fluid.default_main_program().random_seed = 1
+        paddle.static.default_startup_program().random_seed = 1
+        paddle.static.default_main_program().random_seed = 1
 
         dataset1 = RandomDataset(10)
         dataset2 = RandomDataset(10)
@@ -110,10 +109,104 @@ class TestComposeDataset(unittest.TestCase):
             assert np.allclose(label2, label2_t)
 
 
+class TestRandomSplitApi(unittest.TestCase):
+    def test_main(self):
+        paddle.static.default_startup_program().random_seed = 1
+        paddle.static.default_main_program().random_seed = 1
+
+        dataset1, dataset2 = paddle.io.random_split(range(5), [1, 4])
+
+        self.assertTrue(len(dataset1) == 1)
+        self.assertTrue(len(dataset2) == 4)
+
+        elements_list = list(range(5))
+
+        for _, val in enumerate(dataset1):
+            elements_list.remove(val)
+
+        for _, val in enumerate(dataset2):
+            elements_list.remove(val)
+
+        self.assertTrue(len(elements_list) == 0)
+
+
+class TestRandomSplitError(unittest.TestCase):
+    def test_errors(self):
+        paddle.static.default_startup_program().random_seed = 1
+        paddle.static.default_main_program().random_seed = 1
+
+        self.assertRaises(ValueError, paddle.io.random_split, range(5), [3, 8])
+        self.assertRaises(ValueError, paddle.io.random_split, range(5), [8])
+        self.assertRaises(ValueError, paddle.io.random_split, range(5), [])
+
+
+class TestSubsetDataset(unittest.TestCase):
+    def run_main(self, num_workers, places):
+        paddle.static.default_startup_program().random_seed = 1
+        paddle.static.default_main_program().random_seed = 1
+
+        input_np = np.random.random([5, 3, 4]).astype('float32')
+        input = paddle.to_tensor(input_np)
+        label_np = np.random.random([5, 1]).astype('int32')
+        label = paddle.to_tensor(label_np)
+
+        dataset = TensorDataset([input, label])
+        even_subset = paddle.io.Subset(dataset, [0, 2, 4])
+        odd_subset = paddle.io.Subset(dataset, [1, 3])
+
+        assert len(dataset) == 5
+
+        def prepare_dataloader(dataset):
+            return DataLoader(
+                dataset,
+                places=places,
+                num_workers=num_workers,
+                batch_size=1,
+                drop_last=True)
+
+        dataloader = prepare_dataloader(dataset)
+        dataloader_even = prepare_dataloader(even_subset)
+        dataloader_odd = prepare_dataloader(odd_subset)
+
+        def assert_basic(input, label):
+            assert len(input) == 1
+            assert len(label) == 1
+            assert input.shape == [1, 3, 4]
+            assert label.shape == [1, 1]
+            assert isinstance(input, paddle.Tensor)
+            assert isinstance(label, paddle.Tensor)
+
+        elements_list = list()
+        for _, (input, label) in enumerate(dataloader()):
+            assert_basic(input, label)
+            elements_list.append(label)
+
+        for _, (input, label) in enumerate(dataloader_even()):
+            assert_basic(input, label)
+            elements_list.remove(label)
+
+        odd_list = list()
+        for _, (input, label) in enumerate(dataloader_odd()):
+            assert_basic(input, label)
+            odd_list.append(label)
+
+        self.assertEqual(odd_list, elements_list)
+
+    def test_main(self):
+        paddle.static.default_startup_program().random_seed = 1
+        paddle.static.default_main_program().random_seed = 1
+
+        places = [paddle.CPUPlace()]
+        if paddle.is_compiled_with_cuda():
+            places.append(paddle.CUDAPlace(0))
+        for p in places:
+            self.run_main(num_workers=0, places=p)
+
+
 class TestChainDataset(unittest.TestCase):
     def run_main(self, num_workers, places):
-        fluid.default_startup_program().random_seed = 1
-        fluid.default_main_program().random_seed = 1
+        paddle.static.default_startup_program().random_seed = 1
+        paddle.static.default_main_program().random_seed = 1
 
         dataset1 = RandomIterableDataset(10)
         dataset2 = RandomIterableDataset(10)
@@ -135,9 +228,9 @@ class TestChainDataset(unittest.TestCase):
             idx += 1
 
     def test_main(self):
-        places = [fluid.CPUPlace()]
-        if fluid.core.is_compiled_with_cuda():
-            places.append(fluid.CUDAPlace(0))
+        places = [paddle.CPUPlace()]
+        if paddle.is_compiled_with_cuda():
+            places.append(paddle.CUDAPlace(0))
         for p in places:
             self.run_main(num_workers=0, places=p)
 

python/paddle/io/__init__.py

@@ -28,9 +28,11 @@ __all__ = [
     'SequenceSampler',
     'RandomSampler',
     'WeightedRandomSampler',
+    'random_split',
+    'Subset'
 ]
 
 from ..fluid.io import DataLoader
 from ..fluid.dataloader import Dataset, IterableDataset, BatchSampler, get_worker_info, \
         TensorDataset, Sampler, SequenceSampler, RandomSampler, DistributedBatchSampler, \
-        ComposeDataset, ChainDataset, WeightedRandomSampler
+        ComposeDataset, ChainDataset, WeightedRandomSampler, Subset, random_split