Source code for

import torch
from torch._six import int_classes as _int_classes

[docs]class Sampler(object): r"""Base class for all Samplers. Every Sampler subclass has to provide an __iter__ method, providing a way to iterate over indices of dataset elements, and a __len__ method that returns the length of the returned iterators. """ def __init__(self, data_source): pass def __iter__(self): raise NotImplementedError def __len__(self): raise NotImplementedError
[docs]class SequentialSampler(Sampler): r"""Samples elements sequentially, always in the same order. Arguments: data_source (Dataset): dataset to sample from """ def __init__(self, data_source): self.data_source = data_source def __iter__(self): return iter(range(len(self.data_source))) def __len__(self): return len(self.data_source)
[docs]class RandomSampler(Sampler): r"""Samples elements randomly. If without replacement, then sample from a shuffled dataset. If with replacement, then user can specify ``num_samples`` to draw. Arguments: data_source (Dataset): dataset to sample from num_samples (int): number of samples to draw, default=len(dataset) replacement (bool): samples are drawn with replacement if ``True``, default=False """ def __init__(self, data_source, replacement=False, num_samples=None): self.data_source = data_source self.replacement = replacement self.num_samples = num_samples if self.num_samples is not None and replacement is False: raise ValueError("With replacement=False, num_samples should not be specified, " "since a random permute will be performed.") if self.num_samples is None: self.num_samples = len(self.data_source) if not isinstance(self.num_samples, int) or self.num_samples <= 0: raise ValueError("num_samples should be a positive integeral " "value, but got num_samples={}".format(self.num_samples)) if not isinstance(self.replacement, bool): raise ValueError("replacement should be a boolean value, but got " "replacement={}".format(self.replacement)) def __iter__(self): n = len(self.data_source) if self.replacement: return iter(torch.randint(high=n, size=(self.num_samples,), dtype=torch.int64).tolist()) return iter(torch.randperm(n).tolist()) def __len__(self): return len(self.data_source)
[docs]class SubsetRandomSampler(Sampler): r"""Samples elements randomly from a given list of indices, without replacement. Arguments: indices (sequence): a sequence of indices """ def __init__(self, indices): self.indices = indices def __iter__(self): return (self.indices[i] for i in torch.randperm(len(self.indices))) def __len__(self): return len(self.indices)
[docs]class WeightedRandomSampler(Sampler): r"""Samples elements from [0,..,len(weights)-1] with given probabilities (weights). Arguments: weights (sequence) : a sequence of weights, not necessary summing up to one num_samples (int): number of samples to draw replacement (bool): if ``True``, samples are drawn with replacement. If not, they are drawn without replacement, which means that when a sample index is drawn for a row, it cannot be drawn again for that row. """ def __init__(self, weights, num_samples, replacement=True): if not isinstance(num_samples, _int_classes) or isinstance(num_samples, bool) or \ num_samples <= 0: raise ValueError("num_samples should be a positive integeral " "value, but got num_samples={}".format(num_samples)) if not isinstance(replacement, bool): raise ValueError("replacement should be a boolean value, but got " "replacement={}".format(replacement)) self.weights = torch.tensor(weights, dtype=torch.double) self.num_samples = num_samples self.replacement = replacement def __iter__(self): return iter(torch.multinomial(self.weights, self.num_samples, self.replacement).tolist()) def __len__(self): return self.num_samples
[docs]class BatchSampler(Sampler): r"""Wraps another sampler to yield a mini-batch of indices. Args: sampler (Sampler): Base sampler. batch_size (int): Size of mini-batch. drop_last (bool): If ``True``, the sampler will drop the last batch if its size would be less than ``batch_size`` Example: >>> list(BatchSampler(SequentialSampler(range(10)), batch_size=3, drop_last=False)) [[0, 1, 2], [3, 4, 5], [6, 7, 8], [9]] >>> list(BatchSampler(SequentialSampler(range(10)), batch_size=3, drop_last=True)) [[0, 1, 2], [3, 4, 5], [6, 7, 8]] """ def __init__(self, sampler, batch_size, drop_last): if not isinstance(sampler, Sampler): raise ValueError("sampler should be an instance of " ", but got sampler={}" .format(sampler)) if not isinstance(batch_size, _int_classes) or isinstance(batch_size, bool) or \ batch_size <= 0: raise ValueError("batch_size should be a positive integeral value, " "but got batch_size={}".format(batch_size)) if not isinstance(drop_last, bool): raise ValueError("drop_last should be a boolean value, but got " "drop_last={}".format(drop_last)) self.sampler = sampler self.batch_size = batch_size self.drop_last = drop_last def __iter__(self): batch = [] for idx in self.sampler: batch.append(idx) if len(batch) == self.batch_size: yield batch batch = [] if len(batch) > 0 and not self.drop_last: yield batch def __len__(self): if self.drop_last: return len(self.sampler) // self.batch_size else: return (len(self.sampler) + self.batch_size - 1) // self.batch_size


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