CountVectorizer

CountVectorizer(, input='content', encoding='utf-8', decode_error='strict', strip_accents=None, lowercase=True, preprocessor=None, tokenizer=None, stop_words=None, token_pattern='(?u)\b\w\w+\b', ngram_range=(1, 1), analyzer='word', max_df=1.0, min_df=1, max_features=None, vocabulary=None, binary=False, dtype=)*

Convert a collection of text documents to a matrix of token counts

This implementation produces a sparse representation of the counts using scipy.sparse.csr_matrix.

If you do not provide an a-priori dictionary and you do not use an analyzer that does some kind of feature selection then the number of features will be equal to the vocabulary size found by analyzing the data.

Read more in the :ref:User Guide <text_feature_extraction>.

Parameters

• input : string {'filename', 'file', 'content'}, default='content'

  If 'filename', the sequence passed as an argument to fit is expected to be a list of filenames that need reading to fetch the raw content to analyze.

  If 'file', the sequence items must have a 'read' method (file-like object) that is called to fetch the bytes in memory.

  Otherwise the input is expected to be a sequence of items that can be of type string or byte.

• encoding : string, default='utf-8'

  If bytes or files are given to analyze, this encoding is used to decode.

• decode_error : {'strict', 'ignore', 'replace'}, default='strict'

  Instruction on what to do if a byte sequence is given to analyze that contains characters not of the given encoding. By default, it is 'strict', meaning that a UnicodeDecodeError will be raised. Other values are 'ignore' and 'replace'.

• strip_accents : {'ascii', 'unicode'}, default=None

  Remove accents and perform other character normalization during the preprocessing step. 'ascii' is a fast method that only works on characters that have an direct ASCII mapping. 'unicode' is a slightly slower method that works on any characters. None (default) does nothing.

  Both 'ascii' and 'unicode' use NFKD normalization from :func:unicodedata.normalize.

• lowercase : bool, default=True

  Convert all characters to lowercase before tokenizing.

• preprocessor : callable, default=None

  Override the preprocessing (string transformation) stage while preserving the tokenizing and n-grams generation steps. Only applies if analyzer is not callable.

• tokenizer : callable, default=None

  Override the string tokenization step while preserving the preprocessing and n-grams generation steps. Only applies if analyzer == 'word'.

• stop_words : string {'english'}, list, default=None

  If 'english', a built-in stop word list for English is used. There are several known issues with 'english' and you should consider an alternative (see :ref:stop_words).

  If a list, that list is assumed to contain stop words, all of which will be removed from the resulting tokens. Only applies if analyzer == 'word'.

  If None, no stop words will be used. max_df can be set to a value in the range [0.7, 1.0) to automatically detect and filter stop words based on intra corpus document frequency of terms.

• token_pattern : string

  Regular expression denoting what constitutes a "token", only used if analyzer == 'word'. The default regexp select tokens of 2 or more alphanumeric characters (punctuation is completely ignored and always treated as a token separator).

• ngram_range : tuple (min_n, max_n), default=(1, 1)

  The lower and upper boundary of the range of n-values for different word n-grams or char n-grams to be extracted. All values of n such such that min_n <= n <= max_n will be used. For example an ngram_range of (1, 1) means only unigrams, (1, 2) means unigrams and bigrams, and (2, 2) means only bigrams. Only applies if analyzer is not callable.

• analyzer : string, {'word', 'char', 'char_wb'} or callable, default='word'

  Whether the feature should be made of word n-gram or character n-grams. Option 'char_wb' creates character n-grams only from text inside word boundaries; n-grams at the edges of words are padded with space.

  If a callable is passed it is used to extract the sequence of features out of the raw, unprocessed input.

  .. versionchanged:: 0.21

  Since v0.21, if input is filename or file, the data is first read from the file and then passed to the given callable analyzer.

• max_df : float in range [0.0, 1.0] or int, default=1.0

  When building the vocabulary ignore terms that have a document frequency strictly higher than the given threshold (corpus-specific stop words). If float, the parameter represents a proportion of documents, integer absolute counts. This parameter is ignored if vocabulary is not None.

• min_df : float in range [0.0, 1.0] or int, default=1

  When building the vocabulary ignore terms that have a document frequency strictly lower than the given threshold. This value is also called cut-off in the literature. If float, the parameter represents a proportion of documents, integer absolute counts. This parameter is ignored if vocabulary is not None.

• max_features : int, default=None

  If not None, build a vocabulary that only consider the top max_features ordered by term frequency across the corpus.

  This parameter is ignored if vocabulary is not None.

• vocabulary : Mapping or iterable, default=None

  Either a Mapping (e.g., a dict) where keys are terms and values are indices in the feature matrix, or an iterable over terms. If not given, a vocabulary is determined from the input documents. Indices in the mapping should not be repeated and should not have any gap between 0 and the largest index.

• binary : bool, default=False

  If True, all non zero counts are set to 1. This is useful for discrete probabilistic models that model binary events rather than integer counts.

• dtype : type, default=np.int64

  Type of the matrix returned by fit_transform() or transform().

Attributes

• vocabulary_ : dict

  A mapping of terms to feature indices.

  fixed_vocabulary_: boolean True if a fixed vocabulary of term to indices mapping is provided by the user

• stop_words_ : set

  Terms that were ignored because they either:

  • occurred in too many documents (max_df)
  • occurred in too few documents (min_df)
  • were cut off by feature selection (max_features).

  This is only available if no vocabulary was given.

Examples

>>> from sklearn.feature_extraction.text import CountVectorizer
>>> corpus = [
...     'This is the first document.',
...     'This document is the second document.',
...     'And this is the third one.',
...     'Is this the first document?',
... ]
>>> vectorizer = CountVectorizer()
>>> X = vectorizer.fit_transform(corpus)
>>> print(vectorizer.get_feature_names())
['and', 'document', 'first', 'is', 'one', 'second', 'the', 'third', 'this']
>>> print(X.toarray())
[[0 1 1 1 0 0 1 0 1]
[0 2 0 1 0 1 1 0 1]
[1 0 0 1 1 0 1 1 1]
[0 1 1 1 0 0 1 0 1]]
>>> vectorizer2 = CountVectorizer(analyzer='word', ngram_range=(2, 2))
>>> X2 = vectorizer2.fit_transform(corpus)
>>> print(vectorizer2.get_feature_names())
['and this', 'document is', 'first document', 'is the', 'is this',
'second document', 'the first', 'the second', 'the third', 'third one',
'this document', 'this is', 'this the']
>>> print(X2.toarray())
[[0 0 1 1 0 0 1 0 0 0 0 1 0]
[0 1 0 1 0 1 0 1 0 0 1 0 0]
[1 0 0 1 0 0 0 0 1 1 0 1 0]
[0 0 1 0 1 0 1 0 0 0 0 0 1]]

See Also

HashingVectorizer, TfidfVectorizer

Notes

The stop_words_ attribute can get large and increase the model size when pickling. This attribute is provided only for introspection and can be safely removed using delattr or set to None before pickling.

Methods

---

build_analyzer()

Return a callable that handles preprocessing, tokenization and n-grams generation.

Returns

analyzer: callable A function to handle preprocessing, tokenization and n-grams generation.

---

build_preprocessor()

Return a function to preprocess the text before tokenization.

Returns

preprocessor: callable A function to preprocess the text before tokenization.

---

build_tokenizer()

Return a function that splits a string into a sequence of tokens.

Returns

tokenizer: callable A function to split a string into a sequence of tokens.

---

decode(doc)

Decode the input into a string of unicode symbols.

The decoding strategy depends on the vectorizer parameters.

Parameters

• doc : str

  The string to decode.

Returns

doc: str A string of unicode symbols.

---

fit(raw_documents, y=None)

Learn a vocabulary dictionary of all tokens in the raw documents.

Parameters

• raw_documents : iterable

  An iterable which yields either str, unicode or file objects.

Returns

self

---

fit_transform(raw_documents, y=None)

Learn the vocabulary dictionary and return document-term matrix.

This is equivalent to fit followed by transform, but more efficiently implemented.

Parameters

• raw_documents : iterable

  An iterable which yields either str, unicode or file objects.

Returns

• X : array of shape (n_samples, n_features)

  Document-term matrix.

---

get_feature_names()

Array mapping from feature integer indices to feature name.

Returns

• feature_names : list

  A list of feature names.

---

get_params(deep=True)

Get parameters for this estimator.

Parameters

• deep : bool, default=True

  If True, will return the parameters for this estimator and contained subobjects that are estimators.

Returns

• params : mapping of string to any

  Parameter names mapped to their values.

---

get_stop_words()

Build or fetch the effective stop words list.

Returns

stop_words: list or None A list of stop words.

---

inverse_transform(X)

Return terms per document with nonzero entries in X.

Parameters

• X : {array-like, sparse matrix} of shape (n_samples, n_features)

  Document-term matrix.

Returns

• X_inv : list of arrays of shape (n_samples,)

  List of arrays of terms.

---

set_params(params)

Set the parameters of this estimator.

The method works on simple estimators as well as on nested objects (such as pipelines). The latter have parameters of the form <component>__<parameter> so that it's possible to update each component of a nested object.

Parameters

• **params : dict

  Estimator parameters.

Returns

• self : object

  Estimator instance.

---

transform(raw_documents)

Transform documents to document-term matrix.

Extract token counts out of raw text documents using the vocabulary fitted with fit or the one provided to the constructor.

Parameters

• raw_documents : iterable

  An iterable which yields either str, unicode or file objects.

Returns

• X : sparse matrix of shape (n_samples, n_features)

  Document-term matrix.