# -*- coding: utf-8 -*-
"""One-class SVM detector. Implemented on scikit-learn library.
"""
# Author: Yue Zhao <zhaoy@cmu.edu>
# License: BSD 2 clause
from __future__ import division
from __future__ import print_function
from sklearn.svm import OneClassSVM
from sklearn.utils import check_array
from sklearn.utils.validation import check_is_fitted
from .base import BaseDetector
from ..utils.utility import invert_order
[docs]
class OCSVM(BaseDetector):
"""Wrapper of scikit-learn one-class SVM Class with more functionalities.
Unsupervised Outlier Detection.
Estimate the support of a high-dimensional distribution.
The implementation is based on libsvm.
See http://scikit-learn.org/stable/modules/svm.html#svm-outlier-detection
and :cite:`scholkopf2001estimating`.
Parameters
----------
kernel : string, optional (default='rbf')
Specifies the kernel type to be used in the algorithm.
It must be one of 'linear', 'poly', 'rbf', 'sigmoid', 'precomputed' or
a callable.
If none is given, 'rbf' will be used. If a callable is given it is
used to precompute the kernel matrix.
nu : float, optional
An upper bound on the fraction of training
errors and a lower bound of the fraction of support
vectors. Should be in the interval (0, 1]. By default 0.5
will be taken.
degree : int, optional (default=3)
Degree of the polynomial kernel function ('poly').
Ignored by all other kernels.
gamma : float, optional (default='auto')
Kernel coefficient for 'rbf', 'poly' and 'sigmoid'.
If gamma is 'auto' then 1/n_features will be used instead.
coef0 : float, optional (default=0.0)
Independent term in kernel function.
It is only significant in 'poly' and 'sigmoid'.
tol : float, optional
Tolerance for stopping criterion.
shrinking : bool, optional
Whether to use the shrinking heuristic.
cache_size : float, optional
Specify the size of the kernel cache (in MB).
verbose : bool, default: False
Enable verbose output. Note that this setting takes advantage of a
per-process runtime setting in libsvm that, if enabled, may not work
properly in a multithreaded context.
max_iter : int, optional (default=-1)
Hard limit on iterations within solver, or -1 for no limit.
contamination : float in (0., 0.5), optional (default=0.1)
The amount of contamination of the data set, i.e.
the proportion of outliers in the data set. Used when fitting to
define the threshold on the decision function.
Attributes
----------
support_ : array-like, shape = [n_SV]
Indices of support vectors.
support_vectors_ : array-like, shape = [nSV, n_features]
Support vectors.
dual_coef_ : array, shape = [1, n_SV]
Coefficients of the support vectors in the decision function.
coef_ : array, shape = [1, n_features]
Weights assigned to the features (coefficients in the primal
problem). This is only available in the case of a linear kernel.
`coef_` is readonly property derived from `dual_coef_` and
`support_vectors_`
intercept_ : array, shape = [1,]
Constant in the decision function.
decision_scores_ : numpy array of shape (n_samples,)
The outlier scores of the training data.
The higher, the more abnormal. Outliers tend to have higher
scores. This value is available once the detector is fitted.
threshold_ : float
The threshold is based on ``contamination``. It is the
``n_samples * contamination`` most abnormal samples in
``decision_scores_``. The threshold is calculated for generating
binary outlier labels.
labels_ : int, either 0 or 1
The binary labels of the training data. 0 stands for inliers
and 1 for outliers/anomalies. It is generated by applying
``threshold_`` on ``decision_scores_``.
"""
def __init__(self, kernel='rbf', degree=3, gamma='auto', coef0=0.0,
tol=1e-3, nu=0.5, shrinking=True, cache_size=200,
verbose=False, max_iter=-1, contamination=0.1):
super(OCSVM, self).__init__(contamination=contamination)
self.kernel = kernel
self.degree = degree
self.gamma = gamma
self.coef0 = coef0
self.tol = tol
self.nu = nu
self.shrinking = shrinking
self.cache_size = cache_size
self.verbose = verbose
self.max_iter = max_iter
[docs]
def fit(self, X, y=None, sample_weight=None, **params):
"""Fit detector. y is ignored in unsupervised methods.
Parameters
----------
X : numpy array of shape (n_samples, n_features)
The input samples.
y : Ignored
Not used, present for API consistency by convention.
sample_weight : array-like, shape (n_samples,)
Per-sample weights. Rescale C per sample. Higher weights
force the classifier to put more emphasis on these points.
Returns
-------
self : object
Fitted estimator.
"""
# validate inputs X and y (optional)
X = check_array(X)
self._set_n_classes(y)
self.detector_ = OneClassSVM(kernel=self.kernel,
degree=self.degree,
gamma=self.gamma,
coef0=self.coef0,
tol=self.tol,
nu=self.nu,
shrinking=self.shrinking,
cache_size=self.cache_size,
verbose=self.verbose,
max_iter=self.max_iter)
self.detector_.fit(X=X, y=y, sample_weight=sample_weight,
**params)
# invert decision_scores_. Outliers comes with higher outlier scores
self.decision_scores_ = invert_order(
self.detector_.decision_function(X))
self._process_decision_scores()
return self
[docs]
def decision_function(self, X):
"""Predict raw anomaly score of X using the fitted detector.
The anomaly score of an input sample is computed based on different
detector algorithms. For consistency, outliers are assigned with
larger anomaly scores.
Parameters
----------
X : numpy array of shape (n_samples, n_features)
The training input samples. Sparse matrices are accepted only
if they are supported by the base estimator.
Returns
-------
anomaly_scores : numpy array of shape (n_samples,)
The anomaly score of the input samples.
"""
check_is_fitted(self, ['decision_scores_', 'threshold_', 'labels_'])
# Invert outlier scores. Outliers comes with higher outlier scores
return invert_order(self.detector_.decision_function(X))
@property
def support_(self):
"""Indices of support vectors.
Decorator for scikit-learn One class SVM attributes.
"""
return self.detector_.support_
@property
def support_vectors_(self):
"""Support vectors.
Decorator for scikit-learn One class SVM attributes.
"""
return self.detector_.support_vectors_
@property
def dual_coef_(self):
"""Coefficients of the support vectors in the decision function.
Decorator for scikit-learn One class SVM attributes.
"""
return self.detector_.dual_coef_
@property
def coef_(self):
"""Weights assigned to the features (coefficients in the primal
problem). This is only available in the case of a linear kernel.
`coef_` is readonly property derived from `dual_coef_` and
`support_vectors_`
Decorator for scikit-learn One class SVM attributes.
"""
return self.detector_.coef_
@property
def intercept_(self):
""" Constant in the decision function.
Decorator for scikit-learn One class SVM attributes.
"""
return self.detector_.intercept_