SentenceLabelDataset.py

import logging
from typing import List

import numpy as np
from torch.utils.data import IterableDataset

from sentence_transformers.readers import InputExample

logger = logging.getLogger(__name__)


class SentenceLabelDataset(IterableDataset):
    """
    This dataset can be used for some specific Triplet Losses like BATCH_HARD_TRIPLET_LOSS which requires
    multiple examples with the same label in a batch.

    It draws n consecutive, random and unique samples from one label at a time. This is repeated for each label.

    Labels with fewer than n unique samples are ignored.
    This also applied to drawing without replacement, once less than n samples remain for a label, it is skipped.

    This *DOES NOT* check if there are more labels than the batch is large or if the batch size is divisible
    by the samples drawn per label.
    """

    def __init__(self, examples: List[InputExample], samples_per_label: int = 2, with_replacement: bool = False):
        """
        Creates a LabelSampler for a SentenceLabelDataset.

        Args:
            examples (List[InputExample]): A list of InputExamples.
            samples_per_label (int, optional): The number of consecutive, random, and unique samples drawn per label.
                The batch size should be a multiple of samples_per_label. Defaults to 2.
            with_replacement (bool, optional): If True, each sample is drawn at most once (depending on the total number
                of samples per label). If False, one sample can be drawn in multiple draws, but not multiple times in
                the same drawing. Defaults to False.
        """
        super().__init__()

        self.samples_per_label = samples_per_label

        # Group examples by label
        label2ex = {}
        for example in examples:
            if example.label not in label2ex:
                label2ex[example.label] = []
            label2ex[example.label].append(example)

        # Include only labels with at least 2 examples
        self.grouped_inputs = []
        self.groups_right_border = []
        num_labels = 0

        for label, label_examples in label2ex.items():
            if len(label_examples) >= self.samples_per_label:
                self.grouped_inputs.extend(label_examples)
                self.groups_right_border.append(
                    len(self.grouped_inputs)
                )  # At which position does this label group / bucket end?
                num_labels += 1

        self.label_range = np.arange(num_labels)
        self.with_replacement = with_replacement
        np.random.shuffle(self.label_range)

        logger.info(
            "SentenceLabelDataset: {} examples, from which {} examples could be used (those labels appeared at least {} times). {} different labels found.".format(
                len(examples), len(self.grouped_inputs), self.samples_per_label, num_labels
            )
        )

    def __iter__(self):
        label_idx = 0
        count = 0
        already_seen = {}
        while count < len(self.grouped_inputs):
            label = self.label_range[label_idx]
            if label not in already_seen:
                already_seen[label] = set()

            left_border = 0 if label == 0 else self.groups_right_border[label - 1]
            right_border = self.groups_right_border[label]

            if self.with_replacement:
                selection = np.arange(left_border, right_border)
            else:
                selection = [i for i in np.arange(left_border, right_border) if i not in already_seen[label]]

            if len(selection) >= self.samples_per_label:
                for element_idx in np.random.choice(selection, self.samples_per_label, replace=False):
                    count += 1
                    already_seen[label].add(element_idx)
                    yield self.grouped_inputs[element_idx]

            label_idx += 1
            if label_idx >= len(self.label_range):
                label_idx = 0
                already_seen = {}
                np.random.shuffle(self.label_range)

    def __len__(self):
        return len(self.grouped_inputs)