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grouped_batch_sampler.py
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Tue, May 7, 02:23

grouped_batch_sampler.py
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# coding=utf-8
# Copyright 2019-present, the HuggingFace Inc. team and Facebook, Inc.
#
# 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.
""" Adapted from PyTorch Vision (https://github.com/pytorch/vision/blob/master/references/detection/group_by_aspect_ratio.py)
"""
import bisect
import copy
from collections import defaultdict
import numpy as np
from torch.utils.data.sampler import BatchSampler, Sampler
from utils import logger
def _quantize(x, bins):
bins = copy.deepcopy(bins)
bins = sorted(bins)
quantized = list(map(lambda y: bisect.bisect_right(bins, y), x))
return quantized
def create_lengths_groups(lengths, k=0):
bins = np.arange(start=3, stop=k, step=4).tolist() if k > 0 else [10]
groups = _quantize(lengths, bins)
# count number of elements per group
counts = np.unique(groups, return_counts=True)[1]
fbins = [0] + bins + [np.inf]
logger.info("Using {} as bins for aspect lengths quantization".format(fbins))
logger.info("Count of instances per bin: {}".format(counts))
return groups
class GroupedBatchSampler(BatchSampler):
"""
Wraps another sampler to yield a mini-batch of indices.
It enforces that the batch only contain elements from the same group.
It also tries to provide mini-batches which follows an ordering which is
as close as possible to the ordering from the original sampler.
Arguments:
sampler (Sampler): Base sampler.
group_ids (list[int]): If the sampler produces indices in range [0, N),
`group_ids` must be a list of `N` ints which contains the group id of each sample.
The group ids must be a continuous set of integers starting from
0, i.e. they must be in the range [0, num_groups).
batch_size (int): Size of mini-batch.
"""
def __init__(self, sampler, group_ids, batch_size):
if not isinstance(sampler, Sampler):
raise ValueError(
"sampler should be an instance of " "torch.utils.data.Sampler, but got sampler={}".format(sampler)
)
self.sampler = sampler
self.group_ids = group_ids
self.batch_size = batch_size
def __iter__(self):
buffer_per_group = defaultdict(list)
samples_per_group = defaultdict(list)
num_batches = 0
for idx in self.sampler:
group_id = self.group_ids[idx]
buffer_per_group[group_id].append(idx)
samples_per_group[group_id].append(idx)
if len(buffer_per_group[group_id]) == self.batch_size:
yield buffer_per_group[group_id] # TODO
num_batches += 1
del buffer_per_group[group_id]
assert len(buffer_per_group[group_id]) < self.batch_size
# now we have run out of elements that satisfy
# the group criteria, let's return the remaining
# elements so that the size of the sampler is
# deterministic
expected_num_batches = len(self)
num_remaining = expected_num_batches - num_batches
if num_remaining > 0:
# for the remaining batches, group the batches by similar lengths
batch_idx = []
for group_id, idxs in sorted(buffer_per_group.items(), key=lambda x: x[0]):
batch_idx.extend(idxs)
if len(batch_idx) >= self.batch_size:
yield batch_idx[: self.batch_size]
batch_idx = batch_idx[self.batch_size :]
num_remaining -= 1
if len(batch_idx) > 0:
yield batch_idx
num_remaining -= 1
assert num_remaining == 0
def __len__(self):
"""
Return the number of mini-batches rather than the number of samples.
"""
return (len(self.sampler) + self.batch_size - 1) // self.batch_size

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