# TFIDF¶

Computes TF-IDF values from sentences.

The TF-IDF formula is the same one as scikit-learn. The only difference is the fact that the document frequencies are determined online, whereas in a batch setting they can be determined by performing an initial pass through the data.

Note that the parameters are identical to those of feature_extraction.BagOfWords.

## Parameters¶

• normalize – defaults to True

Whether or not the TF-IDF values by their L2 norm.

• on (str) – defaults to None

The name of the feature that contains the text to vectorize. If None, then the input is treated as a document instead of a set of features.

• strip_accents – defaults to True

Whether or not to strip accent characters.

• lowercase – defaults to True

Whether or not to convert all characters to lowercase.

• preprocessor (Callable) – defaults to None

Override the preprocessing step while preserving the tokenizing and n-grams generation steps.

• tokenizer (Callable) – defaults to None

A function used to convert preprocessed text into a dict of tokens. By default, a regex formula that works well in most cases is used.

• ngram_range – defaults to (1, 1)

The lower and upper boundary of the range n-grams to be extracted. All values of n 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 works if tokenizer is not set to False.

## Attributes¶

• dfs (collections.defaultdict))

Document counts.

• n (int)

Number of scanned documents.

## Examples¶

>>> from river import feature_extraction

>>> tfidf = feature_extraction.TFIDF()

>>> corpus = [
...     'This is the first document.',
...     'This document is the second document.',
...     'And this is the third one.',
...     'Is this the first document?',
... ]

>>> for sentence in corpus:
...     tfidf = tfidf.learn_one(sentence)
...     print(tfidf.transform_one(sentence))
{'this': 0.447, 'is': 0.447, 'the': 0.447, 'first': 0.447, 'document': 0.447}
{'this': 0.333, 'document': 0.667, 'is': 0.333, 'the': 0.333, 'second': 0.469}
{'and': 0.497, 'this': 0.293, 'is': 0.293, 'the': 0.293, 'third': 0.497, 'one': 0.497}
{'is': 0.384, 'this': 0.384, 'the': 0.384, 'first': 0.580, 'document': 0.469}


In the above example, a string is passed to transform_one. You can also indicate which field to access if the string is stored in a dictionary:

>>> tfidf = feature_extraction.TFIDF(on='sentence')

>>> for sentence in corpus:
...     x = {'sentence': sentence}
...     tfidf = tfidf.learn_one(x)
...     print(tfidf.transform_one(x))
{'this': 0.447, 'is': 0.447, 'the': 0.447, 'first': 0.447, 'document': 0.447}
{'this': 0.333, 'document': 0.667, 'is': 0.333, 'the': 0.333, 'second': 0.469}
{'and': 0.497, 'this': 0.293, 'is': 0.293, 'the': 0.293, 'third': 0.497, 'one': 0.497}
{'is': 0.384, 'this': 0.384, 'the': 0.384, 'first': 0.580, 'document': 0.469}


## Methods¶

clone

Return a fresh estimator with the same parameters.

The clone has the same parameters but has not been updated with any data. This works by looking at the parameters from the class signature. Each parameter is either - recursively cloned if it's a River classes. - deep-copied via copy.deepcopy if not. If the calling object is stochastic (i.e. it accepts a seed parameter) and has not been seeded, then the clone will not be idempotent. Indeed, this method's purpose if simply to return a new instance with the same input parameters.

learn_many
learn_one

Update with a set of features x.

A lot of transformers don't actually have to do anything during the learn_one step because they are stateless. For this reason the default behavior of this function is to do nothing. Transformers that however do something during the learn_one can override this method.

Parameters

• x (dict)

Returns

Transformer: self

process_text
transform_many

Transform pandas series of string into term-frequency pandas sparse dataframe.

Parameters

• X (pandas.core.series.Series)
transform_one

Transform a set of features x.

Parameters

• x (dict)

Returns

dict: The transformed values.