Text Preprocessing

[source]

Tokenizer

keras.preprocessing.text.Tokenizer(num_words=None, filters='!"#$%&()*+,-./:;<=>?@[\]^_`{|}~ 
', lower=True, split=' ', char_level=False, oov_token=None)

Text tokenization utility class.

This class allows to vectorize a text corpus, by turning each text into either a sequence of integers (each integer being the index of a token in a dictionary) or into a vector where the coefficient for each token could be binary, based on word count, based on tf-idf...

Arguments

  • num_words: the maximum number of words to keep, based on word frequency. Only the most common num_words words will be kept.
  • filters: a string where each element is a character that will be filtered from the texts. The default is all punctuation, plus tabs and line breaks, minus the ' character.
  • lower: boolean. Whether to convert the texts to lowercase.
  • split: str. Separator for word splitting.
  • char_level: if True, every character will be treated as a token.
  • oov_token: if given, it will be added to word_index and used to replace out-of-vocabulary words during text_to_sequence calls

By default, all punctuation is removed, turning the texts into space-separated sequences of words (words maybe include the ' character). These sequences are then split into lists of tokens. They will then be indexed or vectorized.

0 is a reserved index that won't be assigned to any word.


hashing_trick

keras.preprocessing.text.keras.preprocessing.text.hashing_trick(text, n, hash_function=None, filters='!"#$%&()*+,-./:;<=>?@[\]^_`{|}~   
', lower=True, split=' ')

Converts a text to a sequence of indexes in a fixed-size hashing space.

Arguments

  • text: Input text (string).
  • n: Dimension of the hashing space.
  • hash_function: defaults to python hash function, can be 'md5' or any function that takes in input a string and returns a int. Note that 'hash' is not a stable hashing function, so it is not consistent across different runs, while 'md5' is a stable hashing function.
  • filters: list (or concatenation) of characters to filter out, such as punctuation. Default: !"#$%&()*+,-./:;<=>?@[\]^_{|}~

`, includes basic punctuation, tabs, and newlines.

  • lower: boolean. Whether to set the text to lowercase.
  • split: str. Separator for word splitting.

Returns

A list of integer word indices (unicity non-guaranteed).

0 is a reserved index that won't be assigned to any word.

Two or more words may be assigned to the same index, due to possible collisions by the hashing function. The probability of a collision is in relation to the dimension of the hashing space and the number of distinct objects.


one_hot

keras.preprocessing.text.keras.preprocessing.text.one_hot(text, n, filters='!"#$%&()*+,-./:;<=>?@[\]^_`{|}~ 
', lower=True, split=' ')

One-hot encodes a text into a list of word indexes of size n.

This is a wrapper to the hashing_trick function using hash as the hashing function; unicity of word to index mapping non-guaranteed.

Arguments

  • text: Input text (string).
  • n: int. Size of vocabulary.
  • filters: list (or concatenation) of characters to filter out, such as punctuation. Default: !"#$%&()*+,-./:;<=>?@[\]^_{|}~

`, includes basic punctuation, tabs, and newlines.

  • lower: boolean. Whether to set the text to lowercase.
  • split: str. Separator for word splitting.

Returns

List of integers in [1, n]. Each integer encodes a word (unicity non-guaranteed).


text_to_word_sequence

keras.preprocessing.text.keras.preprocessing.text.text_to_word_sequence(text, filters='!"#$%&()*+,-./:;<=>?@[\]^_`{|}~  
', lower=True, split=' ')

Converts a text to a sequence of words (or tokens).

Arguments

  • text: Input text (string).
  • filters: list (or concatenation) of characters to filter out, such as punctuation. Default: !"#$%&()*+,-./:;<=>?@[\]^_{|}~

`, includes basic punctuation, tabs, and newlines.

  • lower: boolean. Whether to convert the input to lowercase.
  • split: str. Separator for word splitting.

Returns

A list of words (or tokens).