8.5.12. sklearn.decomposition.MiniBatchDictionaryLearning¶
- class sklearn.decomposition.MiniBatchDictionaryLearning(n_atoms, alpha=1, n_iter=1000, fit_algorithm='lars', n_jobs=1, chunk_size=3, shuffle=True, dict_init=None, transform_algorithm='omp', transform_n_nonzero_coefs=None, transform_alpha=None, verbose=False, split_sign=False, random_state=None)¶
Mini-batch dictionary learning
Finds a dictionary (a set of atoms) that can best be used to represent data using a sparse code.
Solves the optimization problem:
(U^*,V^*) = argmin 0.5 || Y - U V ||_2^2 + alpha * || U ||_1 (U,V) with || V_k ||_2 = 1 for all 0 <= k < n_atoms
Parameters : n_atoms : int,
number of dictionary elements to extract
alpha : int,
sparsity controlling parameter
n_iter : int,
total number of iterations to perform
fit_algorithm : {‘lars’, ‘cd’}
lars: uses the least angle regression method to solve the lasso problem (linear_model.lars_path) cd: uses the coordinate descent method to compute the Lasso solution (linear_model.Lasso). Lars will be faster if the estimated components are sparse.
transform_algorithm : {‘lasso_lars’, ‘lasso_cd’, ‘lars’, ‘omp’, ‘threshold’}
Algorithm used to transform the data. lars: uses the least angle regression method (linear_model.lars_path) lasso_lars: uses Lars to compute the Lasso solution lasso_cd: uses the coordinate descent method to compute the Lasso solution (linear_model.Lasso). lasso_lars will be faster if the estimated components are sparse. omp: uses orthogonal matching pursuit to estimate the sparse solution threshold: squashes to zero all coefficients less than alpha from the projection dictionary * X’
transform_n_nonzero_coefs : int, 0.1 * n_features by default
Number of nonzero coefficients to target in each column of the solution. This is only used by algorithm=’lars’ and algorithm=’omp’ and is overridden by alpha in the omp case.
transform_alpha : float, 1. by default
If algorithm=’lasso_lars’ or algorithm=’lasso_cd’, alpha is the penalty applied to the L1 norm. If algorithm=’threshold’, alpha is the absolute value of the threshold below which coefficients will be squashed to zero. If algorithm=’omp’, alpha is the tolerance parameter: the value of the reconstruction error targeted. In this case, it overrides n_nonzero_coefs.
split_sign : bool, False by default
Whether to split the sparse feature vector into the concatenation of its negative part and its positive part. This can improve the performance of downstream classifiers.
n_jobs : int,
number of parallel jobs to run
dict_init : array of shape (n_atoms, n_features),
initial value of the dictionary for warm restart scenarios
verbose : :
degree of verbosity of the printed output
chunk_size : int,
number of samples in each mini-batch
shuffle : bool,
whether to shuffle the samples before forming batches
random_state : int or RandomState
Pseudo number generator state used for random sampling.
See also
SparseCoder, DictionaryLearning, SparsePCA, MiniBatchSparsePCA
Notes
References:
J. Mairal, F. Bach, J. Ponce, G. Sapiro, 2009: Online dictionary learning for sparse coding (http://www.di.ens.fr/sierra/pdfs/icml09.pdf)
Attributes
components_ array, [n_atoms, n_features] components extracted from the data Methods
fit(X[, y]) Fit the model from data in X. fit_transform(X[, y]) Fit to data, then transform it partial_fit(X[, y, iter_offset]) Updates the model using the data in X as a mini-batch. set_params(**params) Set the parameters of the estimator. transform(X[, y]) Encode the data as a sparse combination of the dictionary atoms. - __init__(n_atoms, alpha=1, n_iter=1000, fit_algorithm='lars', n_jobs=1, chunk_size=3, shuffle=True, dict_init=None, transform_algorithm='omp', transform_n_nonzero_coefs=None, transform_alpha=None, verbose=False, split_sign=False, random_state=None)¶
- fit(X, y=None)¶
Fit the model from data in X.
Parameters : X: array-like, shape (n_samples, n_features) :
Training vector, where n_samples in the number of samples and n_features is the number of features.
Returns : self : object
Returns the instance itself.
- fit_transform(X, y=None, **fit_params)¶
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 : X : numpy array of shape [n_samples, n_features]
Training set.
y : numpy array of shape [n_samples]
Target values.
Returns : X_new : numpy array of shape [n_samples, n_features_new]
Transformed array.
Notes
This method just calls fit and transform consecutively, i.e., it is not an optimized implementation of fit_transform, unlike other transformers such as PCA.
- partial_fit(X, y=None, iter_offset=0)¶
Updates the model using the data in X as a mini-batch.
Parameters : X: array-like, shape (n_samples, n_features) :
Training vector, where n_samples in the number of samples and n_features is the number of features.
Returns : self : object
Returns the instance itself.
- set_params(**params)¶
Set the parameters of the estimator.
The method works on simple estimators as well as on nested objects (such as pipelines). The former have parameters of the form <component>__<parameter> so that it’s possible to update each component of a nested object.
Returns : self :
- transform(X, y=None)¶
Encode the data as a sparse combination of the dictionary atoms.
Coding method is determined by the object parameter transform_algorithm.
Parameters : X : array of shape (n_samples, n_features)
Test data to be transformed, must have the same number of features as the data used to train the model.
Returns : X_new : array, shape (n_samples, n_components)
Transformed data