from itertools import combinations
import numpy as np
from sklearn.neighbors import NearestNeighbors
from sklearn.utils.validation import check_is_fitted
from .base import BaseOutlierDetector
__all__ = ['FastABOD']
class FastABOD(BaseOutlierDetector):
"""Fast Angle-Based Outlier Detector (FastABOD).
Parameters
----------
algorithm : str, default 'auto'
Tree algorithm to use. Valid algorithms are
['kd_tree'|'ball_tree'|'auto'].
contamination : float, default 0.1
Proportion of outliers in the data set. Used to define the threshold.
leaf_size : int, default 30
Leaf size of the underlying tree.
metric : str or callable, default 'minkowski'
Distance metric to use.
novelty : bool, default False
If True, you can use predict, decision_function and anomaly_score on
new unseen data and not on the training data.
n_jobs : int, default 1
Number of jobs to run in parallel. If -1, then the number of jobs is
set to the number of CPU cores.
n_neighbors : int, default 20
Number of neighbors.
p : int, default 2
Power parameter for the Minkowski metric.
metric_params : dict, default None
Additioal parameters passed to the requested metric.
Attributes
----------
anomaly_score_ : array-like of shape (n_samples,)
Anomaly score for each training data.
contamination_ : float
Actual proportion of outliers in the data set.
threshold_ : float
Threshold.
n_neighbors_ : int
Actual number of neighbors used for ``kneighbors`` queries.
References
----------
.. [#kriegel11] Kriegel, H.-P., Kroger, P., Schubert, E., and Zimek, A.,
"Interpreting and unifying outlier scores,"
In Proceedings of SDM, pp. 13-24, 2011.
.. [#kriegel08] Kriegel, H.-P., Schubert, M., and Zimek, A.,
"Angle-based outlier detection in high-dimensional data,"
In Proceedings of SIGKDD, pp. 444-452, 2008.
Examples
--------
>>> import numpy as np
>>> from kenchi.outlier_detection import FastABOD
>>> X = np.array([
... [0., 0.], [1., 1.], [2., 0.], [3., -1.], [4., 0.],
... [5., 1.], [6., 0.], [7., -1.], [8., 0.], [1000., 1.]
... ])
>>> det = FastABOD(n_neighbors=3)
>>> det.fit_predict(X)
array([ 1, 1, 1, 1, 1, 1, 1, 1, 1, -1])
"""
@property
def X_(self):
"""array-like of shape (n_samples, n_features): Training data.
"""
return self.estimator_._fit_X
def __init__(
self, algorithm='auto', contamination=0.1, leaf_size=30,
metric='minkowski', novelty=False, n_jobs=1, n_neighbors=20,
p=2, metric_params=None
):
self.algorithm = algorithm
self.contamination = contamination
self.leaf_size = leaf_size
self.metric = metric
self.novelty = novelty
self.n_jobs = n_jobs
self.n_neighbors = n_neighbors
self.p = p
self.metric_params = metric_params
def _check_params(self):
super()._check_params()
if self.n_neighbors <= 2:
raise ValueError(
f'n_neighbors must be greater than 2 '
f'but was {self.n_neighbors}'
)
def _check_array(self, X, **kwargs):
kwargs['ensure_min_features'] = 2
kwargs['ensure_min_samples'] = 4
return super()._check_array(X, **kwargs)
def _check_is_fitted(self):
super()._check_is_fitted()
check_is_fitted(self, ['n_neighbors_', 'X_'])
def _fit(self, X):
n_samples, _ = X.shape
self.n_neighbors_ = np.minimum(self.n_neighbors, n_samples - 1)
self.estimator_ = NearestNeighbors(
algorithm = self.algorithm,
leaf_size = self.leaf_size,
metric = self.metric,
n_jobs = self.n_jobs,
n_neighbors = self.n_neighbors_,
p = self.p,
metric_params = self.metric_params
).fit(X)
self._anomaly_score_min = np.max(
self._anomaly_score(X, regularize=False)
)
return self
def _anomaly_score(self, X, regularize=True):
abof = self._abof(X)
if regularize:
return np.maximum(0., -np.log(abof / self._anomaly_score_min))
else:
return abof
def _abof(self, X):
"""Compute the Angle-Based Outlier Factor (ABOF) for each sample."""
if X is self.X_:
neigh_ind = self.estimator_.kneighbors(return_distance=False)
else:
neigh_ind = self.estimator_.kneighbors(X, return_distance=False)
return np.var([
[
(pa @ pb) / (pa @ pa) / (pb @ pb) for pa, pb in combinations(
X_neigh - query_point, 2
)
] for query_point, X_neigh in zip(X, self.X_[neigh_ind])
], axis=1)
