sklearn.linear_model
.Perceptron¶
- class sklearn.linear_model.Perceptron(*, penalty=None, alpha=0.0001, l1_ratio=0.15, fit_intercept=True, max_iter=1000, tol=0.001, shuffle=True, verbose=0, eta0=1.0, n_jobs=None, random_state=0, early_stopping=False, validation_fraction=0.1, n_iter_no_change=5, class_weight=None, warm_start=False)[source]¶
Linear perceptron classifier.
The implementation is a wrapper around
SGDClassifier
by fixing theloss
andlearning_rate
parameters as:SGDClassifier(loss="perceptron", learning_rate="constant")
Other available parameters are described below and are forwarded to
SGDClassifier
.Read more in the User Guide.
- Parameters:
- penalty{‘l2’,’l1’,’elasticnet’}, default=None
The penalty (aka regularization term) to be used.
- alphafloat, default=0.0001
Constant that multiplies the regularization term if regularization is used.
- l1_ratiofloat, default=0.15
The Elastic Net mixing parameter, with
0 <= l1_ratio <= 1
.l1_ratio=0
corresponds to L2 penalty,l1_ratio=1
to L1. Only used ifpenalty='elasticnet'
.New in version 0.24.
- fit_interceptbool, default=True
Whether the intercept should be estimated or not. If False, the data is assumed to be already centered.
- max_iterint, default=1000
The maximum number of passes over the training data (aka epochs). It only impacts the behavior in the
fit
method, and not thepartial_fit
method.New in version 0.19.
- tolfloat or None, default=1e-3
The stopping criterion. If it is not None, the iterations will stop when (loss > previous_loss - tol).
New in version 0.19.
- shufflebool, default=True
Whether or not the training data should be shuffled after each epoch.
- verboseint, default=0
The verbosity level.
- eta0float, default=1
Constant by which the updates are multiplied.
- n_jobsint, default=None
The number of CPUs to use to do the OVA (One Versus All, for multi-class problems) computation.
None
means 1 unless in ajoblib.parallel_backend
context.-1
means using all processors. See Glossary for more details.- random_stateint, RandomState instance or None, default=0
Used to shuffle the training data, when
shuffle
is set toTrue
. Pass an int for reproducible output across multiple function calls. See Glossary.- early_stoppingbool, default=False
Whether to use early stopping to terminate training when validation score is not improving. If set to True, it will automatically set aside a stratified fraction of training data as validation and terminate training when validation score is not improving by at least
tol
forn_iter_no_change
consecutive epochs.New in version 0.20.
- validation_fractionfloat, default=0.1
The proportion of training data to set aside as validation set for early stopping. Must be between 0 and 1. Only used if early_stopping is True.
New in version 0.20.
- n_iter_no_changeint, default=5
Number of iterations with no improvement to wait before early stopping.
New in version 0.20.
- class_weightdict, {class_label: weight} or “balanced”, default=None
Preset for the class_weight fit parameter.
Weights associated with classes. If not given, all classes are supposed to have weight one.
The “balanced” mode uses the values of y to automatically adjust weights inversely proportional to class frequencies in the input data as
n_samples / (n_classes * np.bincount(y))
.- warm_startbool, default=False
When set to True, reuse the solution of the previous call to fit as initialization, otherwise, just erase the previous solution. See the Glossary.
- Attributes:
- classes_ndarray of shape (n_classes,)
The unique classes labels.
- coef_ndarray of shape (1, n_features) if n_classes == 2 else (n_classes, n_features)
Weights assigned to the features.
- intercept_ndarray of shape (1,) if n_classes == 2 else (n_classes,)
Constants in decision function.
- loss_function_concrete LossFunction
The function that determines the loss, or difference between the output of the algorithm and the target values.
- n_features_in_int
Number of features seen during fit.
New in version 0.24.
- feature_names_in_ndarray of shape (
n_features_in_
,) Names of features seen during fit. Defined only when
X
has feature names that are all strings.New in version 1.0.
- n_iter_int
The actual number of iterations to reach the stopping criterion. For multiclass fits, it is the maximum over every binary fit.
- t_int
Number of weight updates performed during training. Same as
(n_iter_ * n_samples + 1)
.
See also
sklearn.linear_model.SGDClassifier
Linear classifiers (SVM, logistic regression, etc.) with SGD training.
Notes
Perceptron
is a classification algorithm which shares the same underlying implementation withSGDClassifier
. In fact,Perceptron()
is equivalent toSGDClassifier(loss="perceptron", eta0=1, learning_rate="constant", penalty=None)
.References
https://en.wikipedia.org/wiki/Perceptron and references therein.
Examples
>>> from sklearn.datasets import load_digits >>> from sklearn.linear_model import Perceptron >>> X, y = load_digits(return_X_y=True) >>> clf = Perceptron(tol=1e-3, random_state=0) >>> clf.fit(X, y) Perceptron() >>> clf.score(X, y) 0.939...
Methods
Predict confidence scores for samples.
densify
()Convert coefficient matrix to dense array format.
fit
(X, y[, coef_init, intercept_init, ...])Fit linear model with Stochastic Gradient Descent.
Get metadata routing of this object.
get_params
([deep])Get parameters for this estimator.
partial_fit
(X, y[, classes, sample_weight])Perform one epoch of stochastic gradient descent on given samples.
predict
(X)Predict class labels for samples in X.
score
(X, y[, sample_weight])Return the mean accuracy on the given test data and labels.
set_fit_request
(*[, coef_init, ...])Request metadata passed to the
fit
method.set_params
(**params)Set the parameters of this estimator.
set_partial_fit_request
(*[, classes, ...])Request metadata passed to the
partial_fit
method.set_score_request
(*[, sample_weight])Request metadata passed to the
score
method.sparsify
()Convert coefficient matrix to sparse format.
- decision_function(X)[source]¶
Predict confidence scores for samples.
The confidence score for a sample is proportional to the signed distance of that sample to the hyperplane.
- Parameters:
- X{array-like, sparse matrix} of shape (n_samples, n_features)
The data matrix for which we want to get the confidence scores.
- Returns:
- scoresndarray of shape (n_samples,) or (n_samples, n_classes)
Confidence scores per
(n_samples, n_classes)
combination. In the binary case, confidence score forself.classes_[1]
where >0 means this class would be predicted.
- densify()[source]¶
Convert coefficient matrix to dense array format.
Converts the
coef_
member (back) to a numpy.ndarray. This is the default format ofcoef_
and is required for fitting, so calling this method is only required on models that have previously been sparsified; otherwise, it is a no-op.- Returns:
- self
Fitted estimator.
- fit(X, y, coef_init=None, intercept_init=None, sample_weight=None)[source]¶
Fit linear model with Stochastic Gradient Descent.
- Parameters:
- X{array-like, sparse matrix}, shape (n_samples, n_features)
Training data.
- yndarray of shape (n_samples,)
Target values.
- coef_initndarray of shape (n_classes, n_features), default=None
The initial coefficients to warm-start the optimization.
- intercept_initndarray of shape (n_classes,), default=None
The initial intercept to warm-start the optimization.
- sample_weightarray-like, shape (n_samples,), default=None
Weights applied to individual samples. If not provided, uniform weights are assumed. These weights will be multiplied with class_weight (passed through the constructor) if class_weight is specified.
- Returns:
- selfobject
Returns an instance of self.
- 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.
- partial_fit(X, y, classes=None, sample_weight=None)[source]¶
Perform one epoch of stochastic gradient descent on given samples.
Internally, this method uses
max_iter = 1
. Therefore, it is not guaranteed that a minimum of the cost function is reached after calling it once. Matters such as objective convergence, early stopping, and learning rate adjustments should be handled by the user.- Parameters:
- X{array-like, sparse matrix}, shape (n_samples, n_features)
Subset of the training data.
- yndarray of shape (n_samples,)
Subset of the target values.
- classesndarray of shape (n_classes,), default=None
Classes across all calls to partial_fit. Can be obtained by via
np.unique(y_all)
, where y_all is the target vector of the entire dataset. This argument is required for the first call to partial_fit and can be omitted in the subsequent calls. Note that y doesn’t need to contain all labels inclasses
.- sample_weightarray-like, shape (n_samples,), default=None
Weights applied to individual samples. If not provided, uniform weights are assumed.
- Returns:
- selfobject
Returns an instance of self.
- predict(X)[source]¶
Predict class labels for samples in X.
- Parameters:
- X{array-like, sparse matrix} of shape (n_samples, n_features)
The data matrix for which we want to get the predictions.
- Returns:
- y_predndarray of shape (n_samples,)
Vector containing the class labels for each sample.
- score(X, y, sample_weight=None)[source]¶
Return the mean accuracy on the given test data and labels.
In multi-label classification, this is the subset accuracy which is a harsh metric since you require for each sample that each label set be correctly predicted.
- Parameters:
- Xarray-like of shape (n_samples, n_features)
Test samples.
- yarray-like of shape (n_samples,) or (n_samples, n_outputs)
True labels for
X
.- sample_weightarray-like of shape (n_samples,), default=None
Sample weights.
- Returns:
- scorefloat
Mean accuracy of
self.predict(X)
w.r.t.y
.
- set_fit_request(*, coef_init: bool | None | str = '$UNCHANGED$', intercept_init: bool | None | str = '$UNCHANGED$', sample_weight: bool | None | str = '$UNCHANGED$') Perceptron [source]¶
Request metadata passed to the
fit
method.Note that this method is only relevant if
enable_metadata_routing=True
(seesklearn.set_config
). Please see User Guide on how the routing mechanism works.The options for each parameter are:
True
: metadata is requested, and passed tofit
if provided. The request is ignored if metadata is not provided.False
: metadata is not requested and the meta-estimator will not pass it tofit
.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.New 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:
- coef_initstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED
Metadata routing for
coef_init
parameter infit
.- intercept_initstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED
Metadata routing for
intercept_init
parameter infit
.- sample_weightstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED
Metadata routing for
sample_weight
parameter infit
.
- Returns:
- selfobject
The updated object.
- 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.
- set_partial_fit_request(*, classes: bool | None | str = '$UNCHANGED$', sample_weight: bool | None | str = '$UNCHANGED$') Perceptron [source]¶
Request metadata passed to the
partial_fit
method.Note that this method is only relevant if
enable_metadata_routing=True
(seesklearn.set_config
). Please see User Guide on how the routing mechanism works.The options for each parameter are:
True
: metadata is requested, and passed topartial_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 topartial_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.New 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:
- classesstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED
Metadata routing for
classes
parameter inpartial_fit
.- sample_weightstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED
Metadata routing for
sample_weight
parameter inpartial_fit
.
- Returns:
- selfobject
The updated object.
- set_score_request(*, sample_weight: bool | None | str = '$UNCHANGED$') Perceptron [source]¶
Request metadata passed to the
score
method.Note that this method is only relevant if
enable_metadata_routing=True
(seesklearn.set_config
). Please see User Guide on how the routing mechanism works.The options for each parameter are:
True
: metadata is requested, and passed toscore
if provided. The request is ignored if metadata is not provided.False
: metadata is not requested and the meta-estimator will not pass it toscore
.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.New 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:
- sample_weightstr, True, False, or None, default=sklearn.utils.metadata_routing.UNCHANGED
Metadata routing for
sample_weight
parameter inscore
.
- Returns:
- selfobject
The updated object.
- sparsify()[source]¶
Convert coefficient matrix to sparse format.
Converts the
coef_
member to a scipy.sparse matrix, which for L1-regularized models can be much more memory- and storage-efficient than the usual numpy.ndarray representation.The
intercept_
member is not converted.- Returns:
- self
Fitted estimator.
Notes
For non-sparse models, i.e. when there are not many zeros in
coef_
, this may actually increase memory usage, so use this method with care. A rule of thumb is that the number of zero elements, which can be computed with(coef_ == 0).sum()
, must be more than 50% for this to provide significant benefits.After calling this method, further fitting with the partial_fit method (if any) will not work until you call densify.
Examples using sklearn.linear_model.Perceptron
¶
Out-of-core classification of text documents
Comparing various online solvers