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import re |
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from abc import ABC, abstractmethod |
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from typing import Union |
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import inflect |
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import nltk |
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from flair.data import Sentence |
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from flair.models import SequenceTagger |
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__all__ = [ |
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"DropFileExtensions", |
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"DropNonAlpha", |
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"DropShortWords", |
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"DropSpecialCharacters", |
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"DropTokens", |
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"DropURLs", |
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"DropWords", |
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"FilterPOS", |
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"FrequencyMinWordCount", |
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"ReplaceSeparators", |
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"ToLowercase", |
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"ToSingular", |
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] |
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class BaseTextTransform(ABC): |
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"""Base class for string transforms.""" |
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@abstractmethod |
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def __call__(self, text: str) -> str: |
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raise NotImplementedError |
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def __repr__(self) -> str: |
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return f"{self.__class__.__name__}()" |
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class DropFileExtensions(BaseTextTransform): |
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"""Remove file extensions from the input text.""" |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to remove file extensions from. |
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""" |
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text = re.sub(r"\.\w+", "", text) |
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return text |
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class DropNonAlpha(BaseTextTransform): |
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"""Remove non-alpha words from the input text.""" |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to remove non-alpha words from. |
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""" |
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text = re.sub(r"[^a-zA-Z\s]", "", text) |
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return text |
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class DropShortWords(BaseTextTransform): |
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"""Remove short words from the input text. |
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Args: |
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min_length (int): Minimum length of words to keep. |
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""" |
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def __init__(self, min_length) -> None: |
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super().__init__() |
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self.min_length = min_length |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to remove short words from. |
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""" |
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text = " ".join([word for word in text.split() if len(word) >= self.min_length]) |
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return text |
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def __repr__(self) -> str: |
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return f"{self.__class__.__name__}(min_length={self.min_length})" |
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class DropSpecialCharacters(BaseTextTransform): |
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"""Remove special characters from the input text. |
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Special characters are defined as any character that is not a word character, whitespace, |
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hyphen, period, apostrophe, or ampersand. |
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""" |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to remove special characters from. |
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""" |
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text = re.sub(r"[^\w\s\-\.\'\&]", "", text) |
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return text |
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class DropTokens(BaseTextTransform): |
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"""Remove tokens from the input text. |
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Tokens are defined as strings enclosed in angle brackets, e.g. <token>. |
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""" |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to remove tokens from. |
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""" |
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text = re.sub(r"<[^>]+>", "", text) |
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return text |
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class DropURLs(BaseTextTransform): |
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"""Remove URLs from the input text.""" |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to remove URLs from. |
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""" |
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text = re.sub(r"http\S+", "", text) |
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return text |
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class DropWords(BaseTextTransform): |
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"""Remove words from the input text. |
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It is case-insensitive and supports singular and plural forms of the words. |
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""" |
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def __init__(self, words: list[str]) -> None: |
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super().__init__() |
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self.words = words |
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self.pattern = r"\b(?:{})\b".format("|".join(words)) |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to remove words from. |
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""" |
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text = re.sub(self.pattern, "", text, flags=re.IGNORECASE) |
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return text |
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def __repr__(self) -> str: |
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return f"{self.__class__.__name__}(pattern={self.pattern})" |
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class FilterPOS(BaseTextTransform): |
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"""Filter words by POS tags. |
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Args: |
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tags (list): List of POS tags to remove. |
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engine (str): POS tagger to use. Must be one of "nltk" or "flair". Defaults to "nltk". |
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""" |
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def __init__(self, tags: list, engine: str = "nltk") -> None: |
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super().__init__() |
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self.tags = tags |
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self.engine = engine |
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if engine == "nltk": |
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nltk.download("averaged_perceptron_tagger", quiet=True) |
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nltk.download("punkt", quiet=True) |
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self.tagger = lambda x: nltk.pos_tag(nltk.word_tokenize(x)) |
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elif engine == "flair": |
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self.tagger = SequenceTagger.load("flair/pos-english-fast").predict |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to remove words with specific POS tags from. |
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""" |
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if self.engine == "nltk": |
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word_tags = self.tagger(text) |
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text = " ".join([word for word, tag in word_tags if tag not in self.tags]) |
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elif self.engine == "flair": |
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sentence = Sentence(text) |
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self.tagger(sentence) |
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text = " ".join([token.text for token in sentence.tokens if token.tag in self.tags]) |
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return text |
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def __repr__(self) -> str: |
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return f"{self.__class__.__name__}(tags={self.tags}, engine={self.engine})" |
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class FrequencyMinWordCount(BaseTextTransform): |
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"""Keep only words that occur more than a minimum number of times in the input text. |
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If the threshold is too strong and no words pass the threshold, the threshold is reduced to |
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the most frequent word. |
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Args: |
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min_count (int): Minimum number of occurrences of a word to keep. |
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""" |
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def __init__(self, min_count) -> None: |
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super().__init__() |
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self.min_count = min_count |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to remove infrequent words from. |
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""" |
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if self.min_count <= 1: |
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return text |
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words = text.split() |
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word_counts = {word: words.count(word) for word in words} |
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max_word_count = max(word_counts.values() or [0]) |
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min_count = max_word_count if self.min_count > max_word_count else self.min_count |
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text = " ".join([word for word in words if word_counts[word] >= min_count]) |
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return text |
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def __repr__(self) -> str: |
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return f"{self.__class__.__name__}(min_count={self.min_count})" |
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class ReplaceSeparators(BaseTextTransform): |
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"""Replace underscores and dashes with spaces.""" |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to replace separators in. |
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""" |
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text = re.sub(r"[_\-]", " ", text) |
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return text |
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def __repr__(self) -> str: |
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return f"{self.__class__.__name__}()" |
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class RemoveDuplicates(BaseTextTransform): |
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"""Remove duplicate words from the input text.""" |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to remove duplicate words from. |
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""" |
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text = " ".join(list(set(text.split()))) |
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return text |
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class TextCompose: |
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"""Compose several transforms together. |
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It differs from the torchvision.transforms.Compose class in that it applies the transforms to |
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a string instead of a PIL Image or Tensor. In addition, it automatically join the list of |
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input strings into a single string and splits the output string into a list of words. |
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Args: |
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transforms (list): List of transforms to compose. |
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""" |
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def __init__(self, transforms: list[BaseTextTransform]) -> None: |
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self.transforms = transforms |
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def __call__(self, text: Union[str, list[str]]) -> list[str]: |
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""" |
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Args: |
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text (Union[str, list[str]]): Text to transform. |
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""" |
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if isinstance(text, list): |
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text = " ".join(text) |
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for t in self.transforms: |
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text = t(text) |
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return text.split() |
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def __repr__(self) -> str: |
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format_string = self.__class__.__name__ + "(" |
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for t in self.transforms: |
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format_string += "\n" |
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format_string += f" {t}" |
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format_string += "\n)" |
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return format_string |
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class ToLowercase(BaseTextTransform): |
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"""Convert text to lowercase.""" |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to convert to lowercase. |
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""" |
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text = text.lower() |
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return text |
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class ToSingular(BaseTextTransform): |
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"""Convert plural words to singular form.""" |
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def __init__(self) -> None: |
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super().__init__() |
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self.transform = inflect.engine().singular_noun |
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def __call__(self, text: str) -> str: |
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""" |
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Args: |
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text (str): Text to convert to singular form. |
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""" |
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words = text.split() |
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for i, word in enumerate(words): |
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if not word.endswith("s"): |
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continue |
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if word[-2:] in ["ss", "us", "is"]: |
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continue |
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if word[-3:] in ["ies", "oes"]: |
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continue |
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words[i] = self.transform(word) or word |
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text = " ".join(words) |
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return text |
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def __repr__(self) -> str: |
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return f"{self.__class__.__name__}()" |
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def default_vocabulary_transforms() -> TextCompose: |
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"""Preprocess input text with preprocessing transforms.""" |
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words_to_drop = [ |
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"image", |
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"photo", |
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"picture", |
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"thumbnail", |
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"logo", |
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"symbol", |
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"clipart", |
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"portrait", |
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"painting", |
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"illustration", |
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"icon", |
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"profile", |
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] |
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pos_tags = ["NN", "NNS", "NNP", "NNPS", "JJ", "JJR", "JJS", "VBG", "VBN"] |
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transforms = [] |
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transforms.append(DropTokens()) |
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transforms.append(DropURLs()) |
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transforms.append(DropSpecialCharacters()) |
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transforms.append(DropFileExtensions()) |
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transforms.append(ReplaceSeparators()) |
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transforms.append(DropShortWords(min_length=3)) |
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transforms.append(DropNonAlpha()) |
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transforms.append(ToLowercase()) |
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transforms.append(ToSingular()) |
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transforms.append(DropWords(words=words_to_drop)) |
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transforms.append(FrequencyMinWordCount(min_count=2)) |
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transforms.append(FilterPOS(tags=pos_tags, engine="flair")) |
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transforms.append(RemoveDuplicates()) |
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transforms = TextCompose(transforms) |
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return transforms |
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