sklearn.kernel_approximation
.AdditiveChi2Sampler¶
-
class
sklearn.kernel_approximation.
AdditiveChi2Sampler
(*, sample_steps=2, sample_interval=None)[source]¶ Approximate feature map for additive chi2 kernel.
Uses sampling the fourier transform of the kernel characteristic at regular intervals.
Since the kernel that is to be approximated is additive, the components of the input vectors can be treated separately. Each entry in the original space is transformed into 2*sample_steps+1 features, where sample_steps is a parameter of the method. Typical values of sample_steps include 1, 2 and 3.
Optimal choices for the sampling interval for certain data ranges can be computed (see the reference). The default values should be reasonable.
Read more in the User Guide.
- Parameters
- sample_stepsint, default=2
Gives the number of (complex) sampling points.
- sample_intervalfloat, default=None
Sampling interval. Must be specified when sample_steps not in {1,2,3}.
- Attributes
- sample_interval_float
Stored sampling interval. Specified as a parameter if sample_steps not in {1,2,3}.
See also
SkewedChi2Sampler
A Fourier-approximation to a non-additive variant of the chi squared kernel.
sklearn.metrics.pairwise.chi2_kernel
The exact chi squared kernel.
sklearn.metrics.pairwise.additive_chi2_kernel
The exact additive chi squared kernel.
Notes
This estimator approximates a slightly different version of the additive chi squared kernel then
metric.additive_chi2
computes.References
See “Efficient additive kernels via explicit feature maps” A. Vedaldi and A. Zisserman, Pattern Analysis and Machine Intelligence, 2011
Examples
>>> from sklearn.datasets import load_digits >>> from sklearn.linear_model import SGDClassifier >>> from sklearn.kernel_approximation import AdditiveChi2Sampler >>> X, y = load_digits(return_X_y=True) >>> chi2sampler = AdditiveChi2Sampler(sample_steps=2) >>> X_transformed = chi2sampler.fit_transform(X, y) >>> clf = SGDClassifier(max_iter=5, random_state=0, tol=1e-3) >>> clf.fit(X_transformed, y) SGDClassifier(max_iter=5, random_state=0) >>> clf.score(X_transformed, y) 0.9499...
Methods
fit
(X[, y])Set the parameters
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
(X)Apply approximate feature map to X.
-
fit
(X, y=None)[source]¶ Set the parameters
- Parameters
- Xarray-like, shape (n_samples, n_features)
Training data, where n_samples in the number of samples and n_features is the number of features.
- Returns
- selfobject
Returns the transformer.
-
fit_transform
(X, y=None, **fit_params)[source]¶ Fit to data, then transform it.
Fits transformer to
X
andy
with optional parametersfit_params
and returns a transformed version ofX
.- 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_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_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]¶ Apply approximate feature map to X.
- Parameters
- X{array-like, sparse matrix} of shape (n_samples, n_features)
- Returns
- X_new{ndarray, sparse matrix}, shape = (n_samples, n_features * (2*sample_steps + 1))
Whether the return value is an array of sparse matrix depends on the type of the input X.