sampler.py

# Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import collections
import functools
import math
import six

import numpy as np
import paddle.distributed as dist


class SamplerHelper(object):
    """
    SamplerHelper is to help construct iterable sampler used for `DataLoader`. It wraps
    a dataset and uses its :code:`__getitem__`
    Every SamplerHelper subclass has to provide an :meth:`__iter__` method, providing a
    way to iterate over indices of dataset elements, and a :meth:`__len__` method
    that returns the length of the returned iterators.
    Also can be used as batch iterator instead of indices iterator when `iterator`
    yield samples rather than indices by initializing `iterator` with a iterable
    dataset.
    .. note:: The :meth:`__len__` method isn't strictly required by
              :class:`DataLoader`, but is expected in any
              calculation involving the length of a :class:`DataLoader`.
    Args:
        dataset (Dataset): Input dataset for SamplerHelper.
        iterable (collections.Iterable|callable, optional): Iterator of dataset. Default: None.
    """

    # chain sampler
    def __init__(self, dataset, iterable=None):
        self.data_source = dataset
        self.iterable = iterable
        if isinstance(dataset, collections.Iterable) and iterable is None:
            # iterable-style datasets
            self.iterable = dataset

    def __iter__(self):
        if self.iterable is None:
            return iter(range(len(self.data_source)))
        elif isinstance(self.iterable, collections.Iterable):
            return iter(self.iterable)
        elif callable(self.iterable):
            return self.iterable()
        else:
            raise ValueError(
                "`iterable` should be None, instance of Iterable or callable "
                "producing generator.")

    def __len__(self):
        # Allow some samplers have different length with `len(data_source)`,
        # such as batch sampler.
        if hasattr(self, "_length"):
            return self._length
        else:
            return len(self.data_source)

    @property
    def length(self):
        """
        Returns:
            the length of the SamplerHelper.
        """

        # since `len()` only produce integer, use length property to get None
        # for uncertain length. samplers can set length if necessary.
        try:
            length = len(self)
        except Exception:
            length = None
        return length

    @length.setter
    def length(self, length):
        self._length = length

    def apply(self, fn):
        """
        Transformations would be performed. It includes `Shuffle`, `sort`, `fit` and `shard`.
        Args:
            fn (callable): Transformations to be performed. It returns transformed iterable (and data_source).
        Returns:
            SamplerHelper: A new transformed object.
        """
        rs = fn(self)
        if isinstance(rs, (list, tuple)):
            iterable, data_source = rs
        else:
            iterable, data_source = rs, self.data_source
        sampler = type(self)(data_source, iterable)
        return sampler

    def shuffle(self, buffer_size=-1, seed=None):
        """
        Shuffle the dataset according to the given buffer size and random seed.
        Args:
            buffer_size (int): Buffer size for shuffle. if buffer_size < 0 or more than the length of the dataset, 
                buffer_size is the length of the dataset. Default: -1. 
            seed (int, optional): Seed for the random. Default: None.
        Returns:
            SamplerHelper
         """
        if seed is not None:
            random_generator = np.random.RandomState(seed)
        else:  # use the global random generator
            random_generator = np.random

        def _impl():
            buf = []
            for idx in iter(self):
                buf.append(idx)
                if buffer_size > 0 and len(buf) >= buffer_size:
                    random_generator.shuffle(buf)
                    for b in buf:
                        yield b
                    buf = []
            if len(buf) > 0:
                random_generator.shuffle(buf)
                for b in buf:
                    yield b

        return type(self)(self.data_source, _impl)

    def sort(self, cmp=None, key=None, reverse=False, buffer_size=-1):
        """
        Sort samples according to given callable cmp or key.
        Args:
            cmp (callable): The funcation of comparison. Default: None. 
            key (callable): Return element to be compared. Default: None.
            reverse (bool): If True, it means in descending order, and False means in ascending order. Default: False.
            buffer_size (int): Buffer size for sort. If buffer_size < 0 or buffer_size is more than the length of the data, 
                buffer_size will be set to the length of the data. Default: -1.
        Returns:
            SamplerHelper
        """
        if key:
            key_wrapper = (lambda x: key(x, self.data_source))
        elif cmp:
            key_wrapper = functools.cmp_to_key(
                lambda x, y: cmp(x, y, self.data_source))
        else:
            key_wrapper = (lambda x: len(self.data_source[x]))

        def _impl():
            data_source = self.data_source
            buf = []
            for idx in iter(self):
                buf.append(idx)
                if buffer_size > 0 and len(buf) >= buffer_size:
                    buf = sorted(buf, key=key_wrapper, reverse=reverse)
                    for b in buf:
                        yield b
                    buf = []
            if len(buf) > 0:
                buf = sorted(buf, key=key_wrapper, reverse=reverse)
                for b in buf:
                    yield b

        return type(self)(self.data_source, _impl)

    def batch(self, batch_size, drop_last=False, batch_size_fn=None, key=None):
        """
        To produce a BatchSampler.
        Args:
            batch_size (int): Batch size.
            drop_last (bool): Whether to drop the last mini batch. Default:
                False.
            batch_size_fn (callable, optional): It accepts four arguments: 
                index of data source, the length of minibatch, the size of
                minibatch so far and data source, and it returns the size of
                mini batch so far. Actually, the returned value can be anything
                and would used as argument size_so_far in `key`. If None, it
                would return the length of mini match. Default: None.
            key (callable, optional): It accepts the size of minibatch so far
                and the length of minibatch, and returns what to be compared
                with `batch_size`. If None, only the size of mini batch so far
                would be compared with `batch_size`. Default: None.
        Returns:
            SamplerHelper
        """
        _key = lambda size_so_far, minibatch_len: size_so_far

        ori_batch_size_fn = batch_size_fn
        if batch_size_fn is None:
            batch_size_fn = lambda new, count, sofar, data_source: count
        key = _key if key is None else key

        def _impl():
            data_source = self.data_source
            minibatch, size_so_far = [], 0
            for idx in iter(self):
                minibatch.append(idx)
                size_so_far = batch_size_fn(idx,
                                            len(minibatch), size_so_far,
                                            data_source)
                if key(size_so_far, len(minibatch)) == batch_size:
                    yield minibatch
                    minibatch, size_so_far = [], 0
                elif key(size_so_far, len(minibatch)) > batch_size:
                    if len(minibatch) == 1:
                        raise ValueError(
                            "Please increase the value of `batch_size`, or limit the max length of batch."
                        )
                    yield minibatch[:-1]
                    minibatch, size_so_far = minibatch[-1:], batch_size_fn(
                        idx, 1, 0, data_source)
            if minibatch and not drop_last:
                yield minibatch

        sampler = type(self)(self.data_source, _impl)
        if ori_batch_size_fn is None and self.length is not None:
            sampler.length = (self.length + int(not drop_last) *
                              (batch_size - 1)) // batch_size
        else:
            sampler.length = None

        return sampler

    def shard(self, num_replicas=None, rank=None):
        """
        Operates slice using multi GPU.
        Args:
            num_replicas (int, optional): The number of training process, and is also the number of GPU cards used in training. 
                Default: None.
            rank (int, optional): Number of training process. Equal to the value of the environment variable PADDLE_TRAINER_ID.
                Default: None.
        Returns:
            SamplerHelper
        """
        if num_replicas is None:
            num_replicas = dist.get_world_size()
        if rank is None:
            rank = dist.get_rank()

        def _impl():
            for i, idx in enumerate(self):
                if i % num_replicas == rank:
                    yield idx
            if i % num_replicas != num_replicas - 1 and rank > i % num_replicas:
                # use last samples to make it evenly divisible
                yield idx

        sampler = type(self)(self.data_source, _impl)
        if self.length is not None:
            sampler.length = int(math.ceil(self.length * 1.0 / num_replicas))
        else:
            sampler.length = None
        return sampler

    def list(self):
        """
        Produce a sampler with a `listiterator` when calling `iter`. Since `list`
        would fetch all contents at time, thus it can get accurate length.
        Returns:
            SamplerHelper
        """

        def _impl():
            indices = list(iter(self))
            self.length = len(indices)
            return iter(indices)

        return type(self)(self.data_source, _impl)