Source code for nannyml.drift.multivariate.data_reconstruction.calculator

#  Author:   Niels Nuyttens  <>
#            Nikolaos Perrakis  <>
#  License: Apache Software License 2.0

"""Calculates the data reconstruction error on unseen analysis data after fitting on reference data.

This calculator wraps a PCA transformation. It will be fitted on reference data when the `fit` method is called.
On calling the `calculate` method it will perform the inverse transformation on the analysis data and calculate
the euclidian distance between the analysis data and the reconstructed version of it.

This is the data reconstruction error, and it can be used as a measure of drift between
the reference and analysis data sets.


from typing import Dict, List, Optional, Tuple, Union

import numpy as np
import pandas as pd
from category_encoders import CountEncoder
from pandas import MultiIndex
from sklearn.decomposition import PCA
from sklearn.impute import SimpleImputer
from sklearn.preprocessing import StandardScaler

from nannyml.base import AbstractCalculator, _list_missing, _split_features_by_type
from nannyml.chunk import Chunker
from nannyml.drift.multivariate.data_reconstruction.result import Result
from nannyml.exceptions import InvalidArgumentsException
from nannyml.sampling_error import SAMPLING_ERROR_RANGE
from nannyml.thresholds import StandardDeviationThreshold, Threshold, calculate_threshold_values
from nannyml.usage_logging import UsageEvent, log_usage

[docs]class DataReconstructionDriftCalculator(AbstractCalculator): """Multivariate Drift Calculator using PCA Reconstruction Error as a measure of drift.""" def __init__( self, column_names: List[str], timestamp_column_name: Optional[str] = None, n_components: Union[int, float, str] = 0.65, chunk_size: Optional[int] = None, chunk_number: Optional[int] = None, chunk_period: Optional[str] = None, chunker: Optional[Chunker] = None, imputer_categorical: Optional[SimpleImputer] = None, imputer_continuous: Optional[SimpleImputer] = None, threshold: Threshold = StandardDeviationThreshold(), ): """Creates a new DataReconstructionDriftCalculator instance. Parameters: column_names: List[str] A list containing the names of features in the provided data set. All of these features will be used by the multivariate data reconstruction drift calculator to calculate an aggregate drift score. timestamp_column_name: str, default=None The name of the column containing the timestamp of the model prediction. n_components: Union[int, float, str], default=0.65 The n_components parameter as passed to the sklearn.decomposition.PCA constructor. See chunk_size: int, default=None Splits the data into chunks containing `chunks_size` observations. Only one of `chunk_size`, `chunk_number` or `chunk_period` should be given. chunk_number: int, default=None Splits the data into `chunk_number` pieces. Only one of `chunk_size`, `chunk_number` or `chunk_period` should be given. chunk_period: str, default=None Splits the data according to the given period. Only one of `chunk_size`, `chunk_number` or `chunk_period` should be given. chunker: Chunker, default=None The `Chunker` used to split the data sets into a lists of chunks. imputer_categorical: SimpleImputer, default=None The SimpleImputer used to impute categorical features in the data. Defaults to using most_frequent value. imputer_continuous: SimpleImputer, default=None The SimpleImputer used to impute continuous features in the data. Defaults to using mean value. threshold: Threshold, default=StandardDeviationThreshold The threshold you wish to evaluate values on. Defaults to a StandardDeviationThreshold with default options. The other allowed value is ConstantThreshold. Examples: >>> import nannyml as nml >>> # Load synthetic data >>> reference, analysis, _ = nml.load_synthetic_car_loan_dataset() >>> feature_column_names = [ ... 'car_value', ... 'salary_range', ... 'debt_to_income_ratio', ... 'loan_length', ... 'repaid_loan_on_prev_car', ... 'size_of_downpayment', ... 'driver_tenure', >>> ] >>> calc = nml.DataReconstructionDriftCalculator( ... column_names=feature_column_names, ... timestamp_column_name='timestamp', ... chunk_size=5000 >>> ) >>> >>> results = calc.calculate(analysis) >>> figure = results.plot() >>> """ super(DataReconstructionDriftCalculator, self).__init__( chunk_size, chunk_number, chunk_period, chunker, timestamp_column_name ) self.column_names = column_names self.continuous_column_names: List[str] = [] self.categorical_column_names: List[str] = [] self.column_name = 'reconstruction_error' self._n_components = n_components self.threshold = threshold self.lower_threshold_value: Optional[float] self.upper_threshold_value: Optional[float] self.lower_threshold_value_limit: float = 0 if imputer_categorical: if not isinstance(imputer_categorical, SimpleImputer): raise TypeError("imputer_categorical needs to be an instantiated SimpleImputer object.") if imputer_categorical.strategy not in ["most_frequent", "constant"]: raise ValueError("Please use a SimpleImputer strategy appropriate for categorical features.") else: imputer_categorical = SimpleImputer(missing_values=np.nan, strategy='most_frequent') self._imputer_categorical = imputer_categorical if imputer_continuous: if not isinstance(imputer_continuous, SimpleImputer): raise TypeError("imputer_continuous needs to be an instantiated SimpleImputer object.") else: imputer_continuous = SimpleImputer(missing_values=np.nan, strategy='mean') self._imputer_continuous = imputer_continuous self.result: Optional[Result] = None @log_usage(UsageEvent.MULTIVAR_DRIFT_CALC_FIT) def _fit(self, reference_data: pd.DataFrame, *args, **kwargs): """Fits the drift calculator to a set of reference data.""" if reference_data.empty: raise InvalidArgumentsException('data contains no rows. Please provide a valid data set.') _list_missing(self.column_names, reference_data) self.continuous_column_names, self.categorical_column_names = _split_features_by_type( reference_data, self.column_names ) # TODO: We duplicate the reference data 3 times, here. Improve to something more memory efficient? data = reference_data.copy(deep=True) if self.categorical_column_names: data[self.categorical_column_names] = self._imputer_categorical.fit_transform( data[self.categorical_column_names] ) if self.continuous_column_names: data[self.continuous_column_names] = self._imputer_continuous.fit_transform( data[self.continuous_column_names] ) encoder = CountEncoder(cols=self.categorical_column_names, normalize=True) data = encoder.fit_transform(data[self.column_names]).to_numpy() scaler = StandardScaler() data = scaler.fit_transform(data) pca = PCA(n_components=self._n_components, random_state=16) self._encoder: CountEncoder = encoder self._scaler: StandardScaler = scaler self._pca: PCA = pca self.result = self._calculate(data=reference_data)[('chunk', 'period')] = 'reference' return self @log_usage(UsageEvent.MULTIVAR_DRIFT_CALC_RUN) def _calculate(self, data: pd.DataFrame, *args, **kwargs) -> Result: """Calculates the data reconstruction drift for a given data set.""" if data.empty: raise InvalidArgumentsException('data contains no rows. Please provide a valid data set.') _list_missing(self.column_names, data) chunks = self.chunker.split(data, columns=self.column_names) res = pd.DataFrame.from_records( [ { 'key': chunk.key, 'chunk_index': chunk.chunk_index, 'start_index': chunk.start_index, 'end_index': chunk.end_index, 'start_date': chunk.start_datetime, 'end_date': chunk.end_datetime, 'period': 'analysis', **self._calculate_chunk_record(, } for chunk in chunks ] ) multilevel_index = _create_multilevel_index() res.columns = multilevel_index res = res.reset_index(drop=True) if self.result is None: self._set_thresholds(results=res) res = self._populate_thresholds(results=res) self.result = Result( results_data=res, timestamp_column_name=self.timestamp_column_name, column_names=self.column_names, categorical_column_names=self.categorical_column_names, continuous_column_names=self.continuous_column_names, ) else: self.result = self.result.filter(period='reference') res = self._populate_thresholds(results=res) = pd.concat([, res], ignore_index=True) return self.result def _calculate_chunk_record(self, data: pd.DataFrame) -> Dict[str, float]: _size = data.shape[0] rcerr_mean, rcerr_std = self._calculate_dre_results(data) # sampling error based on data distribution on chunk - it's simple std err of mean sampling_error = rcerr_std / np.sqrt(_size) record = {} try: record['reconstruction_error'] = rcerr_mean record['sampling_error'] = sampling_error record['upper_confidence_bound'] = rcerr_mean + SAMPLING_ERROR_RANGE * sampling_error record['lower_confidence_bound'] = np.maximum( rcerr_mean - SAMPLING_ERROR_RANGE * sampling_error, self.lower_threshold_value_limit, ) except Exception as exc: record['reconstruction_error'] = np.nan record['sampling_error'] = np.nan record['upper_confidence_bound'] = np.nan record['lower_confidence_bound'] = np.nan self._logger.error( f"An unexpected error occurred while calculating reconstruction error, returning NaN's: {exc}" ) finally: return record def _calculate_dre_results(self, data: pd.DataFrame) -> Tuple[float, float]: # Impute missing values if self.categorical_column_names: data[self.categorical_column_names] = self._imputer_categorical.transform( data[self.categorical_column_names] ) # noqa: E501 if self.continuous_column_names: data[self.continuous_column_names] = self._imputer_continuous.transform(data[self.continuous_column_names]) data = self._encoder.transform(data[self.column_names]).to_numpy() data = self._scaler.transform(data) tmp = self._pca.transform(data) tmp = self._pca.inverse_transform(tmp) tmp = data - tmp tmp = np.linalg.norm(tmp, axis=1) # std returns nan there is only 1 row return (np.mean(tmp), np.std(tmp, ddof=1)) def _set_thresholds(self, results: pd.DataFrame): lower, upper = calculate_threshold_values( threshold=self.threshold, data=results[(self.column_name, 'value')].to_numpy(), lower_threshold_value_limit=self.lower_threshold_value_limit, upper_threshold_value_limit=None, override_using_none=True, logger=self._logger, metric_name=self.column_name, ) self.lower_threshold_value = lower self.upper_threshold_value = upper def _populate_thresholds(self, results: pd.DataFrame): results[(self.column_name, 'upper_threshold')] = self.upper_threshold_value results[(self.column_name, 'lower_threshold')] = self.lower_threshold_value lower_threshold = float('-inf') if self.lower_threshold_value is None else self.lower_threshold_value upper_threshold = float('inf') if self.upper_threshold_value is None else self.upper_threshold_value results[(self.column_name, 'alert')] = results.apply( lambda row: not (lower_threshold < row[(self.column_name, 'value')] < upper_threshold), axis=1, ) return results
def _create_multilevel_index(): chunk_column_names = ['key', 'chunk_index', 'start_index', 'end_index', 'start_date', 'end_date', 'period'] method_column_names = [ 'value', 'sampling_error', 'upper_confidence_boundary', 'lower_confidence_boundary', ] chunk_tuples = [('chunk', chunk_column_name) for chunk_column_name in chunk_column_names] reconstruction_tuples = [('reconstruction_error', method_column_name) for method_column_name in method_column_names] tuples = chunk_tuples + reconstruction_tuples return MultiIndex.from_tuples(tuples)