class sklearn.feature_extraction.FeatureHasher(n_features=1048576, input_type=’dict’, dtype=<class ‘numpy.float64’>, alternate_sign=True, non_negative=False)
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Implements feature hashing, aka the hashing trick.
This class turns sequences of symbolic feature names (strings) into scipy.sparse matrices, using a hash function to compute the matrix column corresponding to a name. The hash function employed is the signed 32-bit version of Murmurhash3.
Feature names of type byte string are used as-is. Unicode strings are converted to UTF-8 first, but no Unicode normalization is done. Feature values must be (finite) numbers.
This class is a low-memory alternative to DictVectorizer and CountVectorizer, intended for large-scale (online) learning and situations where memory is tight, e.g. when running prediction code on embedded devices.
Read more in the User Guide.
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See also
DictVectorizer
sklearn.preprocessing.OneHotEncoder
>>> from sklearn.feature_extraction import FeatureHasher >>> h = FeatureHasher(n_features=10) >>> D = [{'dog': 1, 'cat':2, 'elephant':4},{'dog': 2, 'run': 5}] >>> f = h.transform(D) >>> f.toarray() array([[ 0., 0., -4., -1., 0., 0., 0., 0., 0., 2.], [ 0., 0., 0., -2., -5., 0., 0., 0., 0., 0.]])
fit ([X, y]) | No-op. |
fit_transform (X[, y]) | Fit to data, then transform it. |
get_params ([deep]) | Get parameters for this estimator. |
set_params (**params) | Set the parameters of this estimator. |
transform (raw_X) | Transform a sequence of instances to a scipy.sparse matrix. |
__init__(n_features=1048576, input_type=’dict’, dtype=<class ‘numpy.float64’>, alternate_sign=True, non_negative=False)
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fit(X=None, y=None)
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No-op.
This method doesn’t do anything. It exists purely for compatibility with the scikit-learn transformer API.
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fit_transform(X, y=None, **fit_params)
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Fit to data, then transform it.
Fits transformer to X and y with optional parameters fit_params and returns a transformed version of X.
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get_params(deep=True)
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Get parameters for this estimator.
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set_params(**params)
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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.
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transform(raw_X)
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Transform a sequence of instances to a scipy.sparse matrix.
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sklearn.feature_extraction.FeatureHasher
© 2007–2018 The scikit-learn developers
Licensed under the 3-clause BSD License.
http://scikit-learn.org/stable/modules/generated/sklearn.feature_extraction.FeatureHasher.html