Source code for alibi_detect.cd.tabular

import numpy as np
from scipy.stats import chi2_contingency, ks_2samp
from typing import Callable, Dict, List, Optional, Tuple, Union
from alibi_detect.cd.base import BaseUnivariateDrift


[docs]class TabularDrift(BaseUnivariateDrift):
[docs] def __init__( self, x_ref: Union[np.ndarray, list], p_val: float = .05, categories_per_feature: Dict[int, Optional[int]] = None, preprocess_x_ref: bool = True, update_x_ref: Optional[Dict[str, int]] = None, preprocess_fn: Optional[Callable] = None, correction: str = 'bonferroni', alternative: str = 'two-sided', n_features: Optional[int] = None, input_shape: Optional[tuple] = None, data_type: Optional[str] = None ) -> None: """ Mixed-type tabular data drift detector with Bonferroni or False Discovery Rate (FDR) correction for multivariate data. Kolmogorov-Smirnov (K-S) univariate tests are applied to continuous numerical data and Chi-Squared (Chi2) univariate tests to categorical data. Parameters ---------- x_ref Data used as reference distribution. p_val p-value used for significance of the K-S and Chi2 test for each feature. If the FDR correction method is used, this corresponds to the acceptable q-value. categories_per_feature Dictionary with as keys the column indices of the categorical features and optionally as values the number of possible categorical values for that feature or a list with the possible values. If you know which features are categorical and simply want to infer the possible values of the categorical feature from the reference data you can pass a Dict[int, NoneType] such as {0: None, 3: None} if features 0 and 3 are categorical. If you also know how many categories are present for a given feature you could pass this in the `categories_per_feature` dict in the Dict[int, int] format, e.g. *{0: 3, 3: 2}*. If you pass N categories this will assume the possible values for the feature are [0, ..., N-1]. You can also explicitly pass the possible categories in the Dict[int, List[int]] format, e.g. {0: [0, 1, 2], 3: [0, 55]}. Note that the categories can be arbitrary int values. preprocess_x_ref Whether to already preprocess and infer categories and frequencies for categorical reference data. update_x_ref Reference data can optionally be updated to the last n instances seen by the detector or via reservoir sampling with size n. For the former, the parameter equals {'last': n} while for reservoir sampling {'reservoir_sampling': n} is passed. preprocess_fn Function to preprocess the data before computing the data drift metrics. Typically a dimensionality reduction technique. correction Correction type for multivariate data. Either 'bonferroni' or 'fdr' (False Discovery Rate). alternative Defines the alternative hypothesis for the K-S tests. Options are 'two-sided', 'less' or 'greater'. n_features Number of features used in the combined K-S/Chi-Squared tests. No need to pass it if no preprocessing takes place. In case of a preprocessing step, this can also be inferred automatically but could be more expensive to compute. input_shape Shape of input data. data_type Optionally specify the data type (tabular, image or time-series). Added to metadata. """ super().__init__( x_ref=x_ref, p_val=p_val, preprocess_x_ref=preprocess_x_ref, update_x_ref=update_x_ref, preprocess_fn=preprocess_fn, correction=correction, n_features=n_features, input_shape=input_shape, data_type=data_type ) self.alternative = alternative self.x_ref_categories, self.cat_vars = {}, [] # no categorical features assumed present if isinstance(categories_per_feature, dict): vals = list(categories_per_feature.values()) int_types = (int, np.int16, np.int32, np.int64) if all(v is None for v in vals): # categories_per_feature = Dict[int, NoneType] x_flat = self.x_ref.reshape(self.x_ref.shape[0], -1) categories_per_feature = {f: list(np.unique(x_flat[:, f])) # type: ignore for f in categories_per_feature.keys()} elif all(isinstance(v, int_types) for v in vals): # categories_per_feature = Dict[int, int] categories_per_feature = {f: list(np.arange(v)) # type: ignore for f, v in categories_per_feature.items()} elif not all(isinstance(v, list) for v in vals) and \ all(isinstance(v, int_types) for val in vals for v in val): # type: ignore raise ValueError('categories_per_feature needs to be None or one of ' 'Dict[int, NoneType], Dict[int, int], Dict[int, List[int]]') self.x_ref_categories = categories_per_feature self.cat_vars = list(self.x_ref_categories.keys())
[docs] def feature_score(self, x_ref: np.ndarray, x: np.ndarray) -> Tuple[np.ndarray, np.ndarray]: """ Compute K-S or Chi-Squared test statistics and p-values per feature. Parameters ---------- x_ref Reference instances to compare distribution with. x Batch of instances. Returns ------- Feature level p-values and K-S or Chi-Squared statistics. """ x_ref = x_ref.reshape(x_ref.shape[0], -1) x = x.reshape(x.shape[0], -1) # apply counts on union of categories per variable in both the reference and test data if self.cat_vars: x_categories = {f: list(np.unique(x[:, f])) for f in self.cat_vars} all_categories = {f: list(set().union(self.x_ref_categories[f], x_categories[f])) # type: ignore for f in self.cat_vars} x_ref_count = self._get_counts(x_ref, all_categories) x_count = self._get_counts(x, all_categories) p_val = np.zeros(self.n_features, dtype=np.float32) dist = np.zeros_like(p_val) for f in range(self.n_features): if f in self.cat_vars: contingency_table = np.vstack((x_ref_count[f], x_count[f])) dist[f], p_val[f], _, _ = chi2_contingency(contingency_table) else: dist[f], p_val[f] = ks_2samp(x_ref[:, f], x[:, f], alternative=self.alternative, mode='asymp') return p_val, dist
def _get_counts(self, x: np.ndarray, categories: Dict[int, List[int]]) -> Dict[int, List[int]]: """ Utility method for getting the counts of categories for each categorical variable. """ return {f: [(x[:, f] == v).sum() for v in vals] for f, vals in categories.items()}