pyod/models/kde.py
# -*- coding: utf-8 -*-
"""Kernel Density Estimation (KDE) for Unsupervised Outlier Detection.
"""
# Author: Akira Tamamori <tamamori5917@gmail.com>
# License: BSD 2 clause
from __future__ import division, print_function
from warnings import warn
from sklearn.neighbors import KernelDensity
from sklearn.utils import check_array
from sklearn.utils.validation import check_is_fitted
from .base import BaseDetector
from ..utils.utility import invert_order
class KDE(BaseDetector):
"""KDE class for outlier detection.
For an observation, its negative log probability density could be viewed
as the outlying score.
See :cite:`latecki2007outlier` for details.
Parameters
----------
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.
bandwidth : float, optional (default=1.0)
The bandwidth of the kernel.
algorithm : {'auto', 'ball_tree', 'kd_tree'}, optional
Algorithm used to compute the kernel density estimator:
- 'ball_tree' will use BallTree
- 'kd_tree' will use KDTree
- 'auto' will attempt to decide the most appropriate algorithm
based on the values passed to :meth:`fit` method.
leaf_size : int, optional (default = 30)
Leaf size passed to BallTree. This can affect the
speed of the construction and query, as well as the memory
required to store the tree. The optimal value depends on the
nature of the problem.
metric : string or callable, default 'minkowski'
metric to use for distance computation. Any metric from scikit-learn
or scipy.spatial.distance can be used.
If metric is a callable function, it is called on each
pair of instances (rows) and the resulting value recorded. The callable
should take two arrays as input and return one value indicating the
distance between them. This works for Scipy's metrics, but is less
efficient than passing the metric name as a string.
Distance matrices are not supported.
Valid values for metric are:
- from scikit-learn: ['cityblock', 'cosine', 'euclidean', 'l1', 'l2',
'manhattan']
- from scipy.spatial.distance: ['braycurtis', 'canberra', 'chebyshev',
'correlation', 'dice', 'hamming', 'jaccard', 'kulsinski',
'mahalanobis', 'matching', 'minkowski', 'rogerstanimoto',
'russellrao', 'seuclidean', 'sokalmichener', 'sokalsneath',
'sqeuclidean', 'yule']
See the documentation for scipy.spatial.distance for details on these
metrics.
metric_params : dict, optional (default = None)
Additional keyword arguments for the metric function.
Attributes
----------
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,
contamination=0.1,
bandwidth=1.0,
algorithm="auto",
leaf_size=30,
metric="minkowski",
metric_params=None,
):
super().__init__(contamination=contamination)
self.bandwidth = bandwidth
self.algorithm = algorithm
self.leaf_size = leaf_size
self.metric = metric
self.metric_params = metric_params
if self.algorithm != "auto" and self.algorithm != "ball_tree":
warn(
"algorithm parameter is deprecated and will be removed "
"in version 0.7.6. By default, ball_tree will be used.",
FutureWarning,
)
self.kde_ = KernelDensity(
bandwidth=self.bandwidth,
algorithm=self.algorithm,
leaf_size=self.leaf_size,
metric=self.metric,
metric_params=self.metric_params,
)
self.decision_scores_ = None
def fit(self, X, y=None):
"""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.
Returns
-------
self : object
Fitted estimator.
"""
# validate inputs X and y (optional)
X = check_array(X)
self._set_n_classes(y)
self.kde_.fit(X)
# invert decision_scores_. Outliers comes with higher outlier scores.
self.decision_scores_ = invert_order(self.kde_.score_samples(X))
self._process_decision_scores()
return self
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_"])
X = check_array(X)
# invert outlier scores. Outliers comes with higher outlier scores.
return invert_order(self.kde_.score_samples(X))