CountVectorizer#

class sklearn.feature_extraction.text.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=<class 'numpy.int64'>)[source]#

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.

For an efficiency comparison of the different feature extractors, see FeatureHasher and DictVectorizer Comparison.

Read more in the User Guide.

Parameters:
input{‘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.

  • If 'content', the input is expected to be a sequence of items that can be of type string or byte.

encodingstr, 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’} or callable, 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 a direct ASCII mapping. ‘unicode’ is a slightly slower method that works on any characters. None (default) means no character normalization is performed.

Both ‘ascii’ and ‘unicode’ use NFKD normalization from unicodedata.normalize.

lowercasebool, default=True

Convert all characters to lowercase before tokenizing.

preprocessorcallable, default=None

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

tokenizercallable, default=None

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

stop_words{‘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 Using 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. In this case, setting max_df to a higher value, such as in the range (0.7, 1.0), can automatically detect and filter stop words based on intra corpus document frequency of terms.

token_patternstr or None, default=r”(?u)\b\w\w+\b”

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).

If there is a capturing group in token_pattern then the captured group content, not the entire match, becomes the token. At most one capturing group is permitted.

ngram_rangetuple (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{‘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.

Changed in version 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_dffloat 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_dffloat 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_featuresint, default=None

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

This parameter is ignored if vocabulary is not None.

vocabularyMapping 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.

binarybool, 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.

dtypedtype, 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_bool

True if a fixed vocabulary of term to indices mapping is provided by the user.

See also

HashingVectorizer

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

TfidfVectorizer

Convert a collection of raw documents to a matrix of TF-IDF features.

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)
>>> vectorizer.get_feature_names_out()
array(['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)
>>> vectorizer2.get_feature_names_out()
array(['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]]
build_analyzer()[source]#

Return a callable to process input data.

The callable handles preprocessing, tokenization, and n-grams generation.

Returns:
analyzer: callable

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

build_preprocessor()[source]#

Return a function to preprocess the text before tokenization.

Returns:
preprocessor: callable

A function to preprocess the text before tokenization.

build_tokenizer()[source]#

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)[source]#

Decode the input into a string of unicode symbols.

The decoding strategy depends on the vectorizer parameters.

Parameters:
docbytes or str

The string to decode.

Returns:
doc: str

A string of unicode symbols.

fit(raw_documents, y=None)[source]#

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

Parameters:
raw_documentsiterable

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

yNone

This parameter is ignored.

Returns:
selfobject

Fitted vectorizer.

fit_transform(raw_documents, y=None)[source]#

Learn the vocabulary dictionary and return document-term matrix.

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

Parameters:
raw_documentsiterable

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

yNone

This parameter is ignored.

Returns:
Xarray of shape (n_samples, n_features)

Document-term matrix.

get_feature_names_out(input_features=None)[source]#

Get output feature names for transformation.

Parameters:
input_featuresarray-like of str or None, default=None

Not used, present here for API consistency by convention.

Returns:
feature_names_outndarray of str objects

Transformed feature names.

get_metadata_routing()[source]#

Get metadata routing of this object.

Please check User Guide on how the routing mechanism works.

Returns:
routingMetadataRequest

A MetadataRequest encapsulating routing information.

get_params(deep=True)[source]#

Get parameters for this estimator.

Parameters:
deepbool, default=True

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

Returns:
paramsdict

Parameter names mapped to their values.

get_stop_words()[source]#

Build or fetch the effective stop words list.

Returns:
stop_words: list or None

A list of stop words.

inverse_transform(X)[source]#

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_invlist of arrays of shape (n_samples,)

List of arrays of terms.

set_fit_request(*, raw_documents: bool | None | str = '$UNCHANGED$') → CountVectorizer[source]#

Request metadata passed to the fit method.

Note that this method is only relevant if enable_metadata_routing=True (see sklearn.set_config). Please see User Guide on how the routing mechanism works.

The options for each parameter are:

  • True: metadata is requested, and passed to fit if provided. The request is ignored if metadata is not provided.

  • False: metadata is not requested and the meta-estimator will not pass it to fit.

  • None: metadata is not requested, and the meta-estimator will raise an error if the user provides it.

  • str: metadata should be passed to the meta-estimator with this given alias instead of the original name.

The default (sklearn.utils.metadata_routing.UNCHANGED) retains the existing request. This allows you to change the request for some parameters and not others.

Added in version 1.3.

Note

This method is only relevant if this estimator is used as a sub-estimator of a meta-estimator, e.g. used inside a Pipeline. Otherwise it has no effect.

Parameters:
raw_documentsstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED

Metadata routing for raw_documents parameter in fit.

Returns:
selfobject

The updated object.

set_params(**params)[source]#

Set the parameters of this estimator.

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

Parameters:
**paramsdict

Estimator parameters.

Returns:
selfestimator instance

Estimator instance.

set_transform_request(*, raw_documents: bool | None | str = '$UNCHANGED$') → CountVectorizer[source]#

Request metadata passed to the transform method.

Note that this method is only relevant if enable_metadata_routing=True (see sklearn.set_config). Please see User Guide on how the routing mechanism works.

The options for each parameter are:

  • True: metadata is requested, and passed to transform if provided. The request is ignored if metadata is not provided.

  • False: metadata is not requested and the meta-estimator will not pass it to transform.

  • None: metadata is not requested, and the meta-estimator will raise an error if the user provides it.

  • str: metadata should be passed to the meta-estimator with this given alias instead of the original name.

The default (sklearn.utils.metadata_routing.UNCHANGED) retains the existing request. This allows you to change the request for some parameters and not others.

Added in version 1.3.

Note

This method is only relevant if this estimator is used as a sub-estimator of a meta-estimator, e.g. used inside a Pipeline. Otherwise it has no effect.

Parameters:
raw_documentsstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED

Metadata routing for raw_documents parameter in transform.

Returns:
selfobject

The updated object.

transform(raw_documents)[source]#

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_documentsiterable

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

Returns:
Xsparse matrix of shape (n_samples, n_features)

Document-term matrix.

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