sklearn.random_projection
.SparseRandomProjection¶

class
sklearn.random_projection.
SparseRandomProjection
(n_components='auto', *, density='auto', eps=0.1, dense_output=False, random_state=None)[source]¶ Reduce dimensionality through sparse random projection.
Sparse random matrix is an alternative to dense random projection matrix that guarantees similar embedding quality while being much more memory efficient and allowing faster computation of the projected data.
If we note
s = 1 / density
the components of the random matrix are drawn from:sqrt(s) / sqrt(n_components) with probability 1 / 2s
0 with probability 1  1 / s
+sqrt(s) / sqrt(n_components) with probability 1 / 2s
Read more in the User Guide.
New in version 0.13.
 Parameters
 n_componentsint or ‘auto’, default=’auto’
Dimensionality of the target projection space.
n_components can be automatically adjusted according to the number of samples in the dataset and the bound given by the JohnsonLindenstrauss lemma. In that case the quality of the embedding is controlled by the
eps
parameter.It should be noted that JohnsonLindenstrauss lemma can yield very conservative estimated of the required number of components as it makes no assumption on the structure of the dataset.
 densityfloat or ‘auto’, default=’auto’
Ratio in the range (0, 1] of nonzero component in the random projection matrix.
If density = ‘auto’, the value is set to the minimum density as recommended by Ping Li et al.: 1 / sqrt(n_features).
Use density = 1 / 3.0 if you want to reproduce the results from Achlioptas, 2001.
 epsfloat, default=0.1
Parameter to control the quality of the embedding according to the JohnsonLindenstrauss lemma when n_components is set to ‘auto’. This value should be strictly positive.
Smaller values lead to better embedding and higher number of dimensions (n_components) in the target projection space.
 dense_outputbool, default=False
If True, ensure that the output of the random projection is a dense numpy array even if the input and random projection matrix are both sparse. In practice, if the number of components is small the number of zero components in the projected data will be very small and it will be more CPU and memory efficient to use a dense representation.
If False, the projected data uses a sparse representation if the input is sparse.
 random_stateint, RandomState instance or None, default=None
Controls the pseudo random number generator used to generate the projection matrix at fit time. Pass an int for reproducible output across multiple function calls. See Glossary.
 Attributes
 n_components_int
Concrete number of components computed when n_components=”auto”.
 components_sparse matrix of shape (n_components, n_features)
Random matrix used for the projection. Sparse matrix will be of CSR format.
 density_float in range 0.0  1.0
Concrete density computed from when density = “auto”.
See also
References
 1
Ping Li, T. Hastie and K. W. Church, 2006, “Very Sparse Random Projections”. https://web.stanford.edu/~hastie/Papers/Ping/KDD06_rp.pdf
 2
D. Achlioptas, 2001, “Databasefriendly random projections”, https://users.soe.ucsc.edu/~optas/papers/jl.pdf
Examples
>>> import numpy as np >>> from sklearn.random_projection import SparseRandomProjection >>> rng = np.random.RandomState(42) >>> X = rng.rand(100, 10000) >>> transformer = SparseRandomProjection(random_state=rng) >>> X_new = transformer.fit_transform(X) >>> X_new.shape (100, 3947) >>> # very few components are nonzero >>> np.mean(transformer.components_ != 0) 0.0100...
Methods
fit
(X[, y])Generate a sparse random projection matrix.
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)Project the data by using matrix product with the random matrix

fit
(X, y=None)[source]¶ Generate a sparse random projection matrix.
 Parameters
 X{ndarray, sparse matrix} of shape (n_samples, n_features)
Training set: only the shape is used to find optimal random matrix dimensions based on the theory referenced in the afore mentioned papers.
 y
Ignored
 Returns
 self

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
 Xarraylike of shape (n_samples, n_features)
Input samples.
 yarraylike 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]¶ Project the data by using matrix product with the random matrix
 Parameters
 X{ndarray, sparse matrix} of shape (n_samples, n_features)
The input data to project into a smaller dimensional space.
 Returns
 X_new{ndarray, sparse matrix} of shape (n_samples, n_components)
Projected array.