MinHashEncoder#

class skrub.MinHashEncoder(*, n_components=30, ngram_range=(2, 4), hashing='fast', minmax_hash=False, n_jobs=None)[source]#

Encode string categorical features by applying the MinHash method to n-gram decompositions of strings.

Note

MinHashEncoder is a type of single-column transformer. Unlike most scikit-learn estimators, its fit, transform and fit_transform methods expect a single column (a pandas or polars Series) rather than a full dataframe. To apply this transformer to one or more columns in a dataframe, use it as a parameter in a skrub.TableVectorizer or sklearn.compose.ColumnTransformer. In the ColumnTransformer, pass a single column: make_column_transformer((MinHashEncoder(), 'col_name_1'), (MinHashEncoder(), 'col_name_2')) instead of make_column_transformer((MinHashEncoder(), ['col_name_1', 'col_name_2'])).

The principle is as follows:

  1. A string is viewed as a succession of numbers (the ASCII or UTF8 representation of its elements).

  2. The string is then decomposed into a set of n-grams, i.e. n-dimensional vectors of integers.

  3. A hashing function is used to assign an integer to each n-gram. The minimum of the hashes over all n-grams is used in the encoding.

  4. This process is repeated with N hashing functions to form N-dimensional encodings.

Maxhash encodings can be computed similarly by taking the maximum hash instead. With this procedure, strings that share many n-grams have a greater probability of having the same encoding value. These encodings thus capture morphological similarities between strings.

Parameters:
n_componentsint, default=30

The number of dimension of encoded strings. Numbers around 300 tend to lead to good prediction performance, but with more computational cost.

ngram_range2-tuple of int, default=(2, 4)

The lower and upper boundaries of the range of n-values for different n-grams used in the string similarity. All values of n such that min_n <= n <= max_n will be used.

hashing{‘fast’, ‘murmur’}, default=’fast’

Hashing function. fast is faster than murmur but might have some concern with its entropy.

minmax_hashbool, default=False

If True, returns the min and max hashes concatenated.

n_jobsint, optional

The number of jobs to run in parallel. The hash computations for all unique elements are parallelized. None means 1 unless in a joblib.parallel_backend. -1 means using all processors. See n_jobs for more details.

Attributes:
hash_dict_LRUDict

Computed hashes.

n_features_in_int

Number of features seen during fit.

feature_names_in_ndarray of shape (n_features_in,)

Names of features seen during fit.

See also

GapEncoder

Encodes dirty categories (strings) by constructing latent topics with continuous encoding.

SimilarityEncoder

Encode string columns as a numeric array with n-gram string similarity.

deduplicate

Deduplicate data by hierarchically clustering similar strings.

References

For a detailed description of the method, see Encoding high-cardinality string categorical variables by Cerda, Varoquaux (2019).

Examples

>>> import pandas as pd
>>> from skrub import MinHashEncoder
>>> enc = MinHashEncoder(n_components=5)

Let’s encode the following non-normalized data:

>>> X = pd.Series(['paris, FR', 'Paris', 'London, UK', 'London'], name='city')
>>> enc.fit(X)
MinHashEncoder(n_components=5)

The encoded data with 5 components are:

>>> enc.transform(X)
         city_0        city_1        city_2        city_3        city_4
0 -1.783375e+09 -1.588270e+09 -1.663592e+09 -1.819887e+09 -1.962594e+09
1 -8.480470e+08 -1.766579e+09 -1.558912e+09 -1.485745e+09 -1.687299e+09
2 -1.975829e+09 -2.095000e+09 -1.596521e+09 -1.817594e+09 -2.095693e+09
3 -1.975829e+09 -2.095000e+09 -1.530721e+09 -1.459183e+09 -1.580988e+09

Methods

fit(X[, y])

Fit the MinHashEncoder to X.

fit_transform(X[, y])

Fit to data, then transform it.

get_feature_names_out()

Get output feature names for transformation.

get_metadata_routing()

Get metadata routing of this object.

get_params([deep])

Get parameters for this estimator.

set_fit_request(*[, column])

Request metadata passed to the fit method.

set_output(*[, transform])

Set output container.

set_params(**params)

Set the parameters of this estimator.

transform(X)

Transform X using specified encoding scheme.
fit(X, y=None)[source]#

Fit the MinHashEncoder to X.

In practice, just initializes a dictionary to store encodings to speed up computation.

Parameters:
Xarray_like, shape (n_samples, ) or (n_samples, n_columns)

The string data to encode. Only here for compatibility.

yNone

Unused, only here for compatibility.

Returns:
MinHashEncoder

The fitted MinHashEncoder instance (self).

fit_transform(X, y=None, **fit_params)[source]#

Fit to data, then transform it.

Fits transformer to X and y with optional parameters fit_params and returns a transformed version of X.

Parameters:
Xarray_like of shape (n_samples, n_features)

Input samples.

yarray_like of shape (n_samples,) or (n_samples, n_outputs), default=None

Target values (None for unsupervised transformations).

**fit_paramsdict

Additional fit parameters.

Returns:
X_newndarray array of shape (n_samples, n_features_new)

Transformed array.

get_feature_names_out()[source]#

Get output feature names for transformation.

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.

set_fit_request(*, column='$UNCHANGED$')[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:
columnstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED

Metadata routing for column parameter in fit.

Returns:
selfobject

The updated object.

set_output(*, transform=None)[source]#

Set output container.

See Introducing the set_output API for an example on how to use the API.

Parameters:
transform{“default”, “pandas”, “polars”}, default=None

Configure output of transform and fit_transform.

  • “default”: Default output format of a transformer

  • “pandas”: DataFrame output

  • “polars”: Polars output

  • None: Transform configuration is unchanged

Added in version 1.4: “polars” option was added.

Returns:
selfestimator instance

Estimator instance.

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.

transform(X)[source]#

Transform X using specified encoding scheme.

Parameters:
Xarray_like, shape (n_samples, ) or (n_samples, n_columns)

The string data to encode.

Returns:
ndarray of shape (n_samples, n_columns * n_components)

Transformed input.