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https://github.com/IBM/ai-privacy-toolkit.git
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a40484e0c9
* Add column distribution comparison, and a third method for dataset assessment by membership classification * Address review comments, add additional distribution comparison tests and make them externally configurable too, in addition to the alpha becoming configurable. Signed-off-by: Maya Anderson <mayaa@il.ibm.com>
233 lines
13 KiB
Python
233 lines
13 KiB
Python
import abc
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from dataclasses import dataclass
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import numpy as np
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from scipy import stats
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from sklearn.neighbors import NearestNeighbors
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from tqdm import tqdm
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from pandas.api.types import is_numeric_dtype, is_categorical_dtype
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from apt.utils.datasets import ArrayDataset
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class AttackStrategyUtils(abc.ABC):
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"""
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Abstract base class for common utilities of various privacy attack strategies.
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"""
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pass
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@dataclass
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class DistributionValidationResult:
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"""Holds the result of the validation of distributions similarities.
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Attributes:
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distributions_validated : False if distribution validation failed for some reason, and no conclusion was drawn
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distributions_valid: False if there are columns whose distribution is different between the datasets
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member_column_distribution_diff (list): Columns whose distribution is different between the member and the
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synthetic datasets
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non_member_column_distribution_diff (list): Columns whose distribution is different between the non-member and
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the synthetic datasets
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"""
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distributions_validated: bool
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distributions_valid: bool
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member_column_distribution_diff: list
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non_member_column_distribution_diff: list
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class KNNAttackStrategyUtils(AttackStrategyUtils):
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"""
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Common utilities for attack strategy based on KNN distances.
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"""
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def __init__(self, use_batches: bool = False, batch_size: int = 10, distribution_comparison_alpha: float = 0.05,
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distribution_comparison_numeric_test: str = 'KS',
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distribution_comparison_categorical_test: str = 'CHI') -> None:
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"""
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:param use_batches: Use batches with a progress meter or not when finding KNNs for query set
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:param batch_size: if use_batches is True, the size of batch_size should be > 0
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:param distribution_comparison_alpha: the significance level of the statistical distribution test pvalue.
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If p-value is less than alpha, then we reject the null hypothesis that the
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observed samples are drawn from the same distribution and we claim that
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the distributions are different.
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:param distribution_comparison_numeric_test: Type of test to compare distributions of numeric columns. Can be:
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'KS' for the two-sample Kolmogorov-Smirnov test for goodness of fit,
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'CVM' for the two-sample Cramér-von Mises test for goodness of fit,
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'AD' for the Anderson-Darling test for 2-samples,
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'ES' for the Epps-Singleton (ES) test statistic. The default is 'KS'
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:param distribution_comparison_categorical_test: Type of test to compare distributions of categorical columns.
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Can be:
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'CHI' for the one-way chi-square test,
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'AD' for The Anderson-Darling test for 2-samples,
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'ES' for the Epps-Singleton (ES) test statistic.
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The default is 'ES'.
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"""
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self.use_batches = use_batches
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self.batch_size = batch_size
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if use_batches:
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if batch_size < 1:
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raise ValueError(f"When using batching batch_size should be > 0, and not {batch_size}")
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self.distribution_comparison_alpha = distribution_comparison_alpha
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self.distribution_comparison_numeric_test = distribution_comparison_numeric_test
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self.distribution_comparison_categorical_test = distribution_comparison_categorical_test
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def fit(self, knn_learner: NearestNeighbors, dataset: ArrayDataset):
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"""
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Fit the KNN learner.
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:param knn_learner: The KNN model to fit.
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:param dataset: The training set to fit the model on.
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"""
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knn_learner.fit(dataset.get_samples())
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def find_knn(self, knn_learner: NearestNeighbors, query_samples: ArrayDataset, distance_processor=None):
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"""
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Nearest neighbor search function.
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:param query_samples: query samples, to which nearest neighbors are to be found
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:param knn_learner: unsupervised learner for implementing neighbor searches, after it was fitted
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:param distance_processor: function for processing the distance into another more relevant metric per sample.
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Its input is an array representing distances (the distances returned by NearestNeighbors.kneighbors() ), and
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the output should be another array with distance-based values that enable to compute the final risk score
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:return:
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distances of the query samples to their nearest neighbors, or a metric based on that distance and calculated
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by the distance_processor function
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"""
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samples = query_samples.get_samples()
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if not self.use_batches:
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distances, _ = knn_learner.kneighbors(samples, return_distance=True)
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if distance_processor:
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return distance_processor(distances)
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else:
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return distances
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distances = []
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for i in tqdm(range(len(samples) // self.batch_size)):
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x_batch = samples[i * self.batch_size:(i + 1) * self.batch_size]
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x_batch = np.reshape(x_batch, [self.batch_size, -1])
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# dist_batch: distance between every query sample in batch to its KNNs among training samples
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dist_batch, _ = knn_learner.kneighbors(x_batch, return_distance=True)
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# The probability of each sample to be generated
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if distance_processor:
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distance_based_metric_per_sample_batch = distance_processor(dist_batch)
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distances.append(distance_based_metric_per_sample_batch)
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else:
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distances.append(dist_batch)
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return np.concatenate(distances)
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@staticmethod
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def _column_statistical_test(df1_column_samples, df2_column_samples, column, is_categorical, is_numeric,
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numeric_test_type, categorical_test_type, alpha, differing_columns):
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if is_categorical:
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test_type = categorical_test_type
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if test_type == 'CHI':
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try:
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result = stats.chisquare(f_obs=df1_column_samples, f_exp=df1_column_samples)
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except ValueError as e:
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if str(e).startswith('For each axis slice, the sum of'):
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print('Column', column, ' the observed and expected sums are not the same,'
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'so cannot run distribution comparison test')
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raise e
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else:
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raise
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elif test_type == 'AD':
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result = stats.anderson_ksamp([df1_column_samples, df2_column_samples], midrank=True)
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elif test_type == 'ES':
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result = stats.epps_singleton_2samp(df1_column_samples, df2_column_samples)
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else:
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raise ValueError('Unknown test type', test_type)
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elif is_numeric:
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test_type = numeric_test_type
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if test_type == 'KS':
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result = stats.ks_2samp(df1_column_samples, df2_column_samples)
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elif test_type == 'CVM':
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result = stats.cramervonmises_2samp(df1_column_samples, df1_column_samples)
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elif test_type == 'AD':
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result = stats.anderson_ksamp([df1_column_samples, df2_column_samples], midrank=True)
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elif test_type == 'ES':
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result = stats.epps_singleton_2samp(df1_column_samples, df2_column_samples)
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else:
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raise ValueError('Unknown test type', test_type)
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else:
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print(f'Skipping non-numeric and non-categorical column {column}')
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return
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print(
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f"{column}: {test_type} = {result.statistic:.4f} "
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f"(p-value = {result.pvalue:.3e}, are equal = {result.pvalue > 0.05})")
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if result.pvalue < alpha:
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# Reject H0, different distributions
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print(f"Distributions differ in column {column}, p-value: {result.pvalue}")
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differing_columns.append(column)
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else:
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# Accept H0, similar distributions
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print(f'Accept H0, similar distributions in column {column}')
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def _columns_different_distributions(self, df1: ArrayDataset, df2: ArrayDataset,
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categorical_features: list = []) -> list:
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differing_columns = []
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df1_samples = df1.get_samples()
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df2_samples = df2.get_samples()
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if df1.is_pandas:
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for name, _ in df1_samples.items():
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is_categorical = name in categorical_features or is_categorical_dtype(df1_samples.dtypes[name])
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is_numeric = is_numeric_dtype(df1_samples.dtypes[name])
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KNNAttackStrategyUtils._column_statistical_test(df1_samples[name], df2_samples[name], name,
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is_categorical, is_numeric,
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self.distribution_comparison_numeric_test,
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self.distribution_comparison_categorical_test,
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self.distribution_comparison_alpha,
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differing_columns)
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else:
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is_numeric = np.issubdtype(df1_samples.dtype, int) or np.issubdtype(df1_samples.dtype, float)
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for i, column in enumerate(df1_samples.T):
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is_categorical = i in categorical_features
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KNNAttackStrategyUtils._column_statistical_test(df1_samples[:, i], df2_samples[:, i], i,
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is_categorical, is_numeric,
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self.distribution_comparison_numeric_test,
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self.distribution_comparison_categorical_test,
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self.distribution_comparison_alpha, differing_columns)
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return differing_columns
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def validate_distributions(self, original_data_members: ArrayDataset, original_data_non_members: ArrayDataset,
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synthetic_data: ArrayDataset, categorical_features: list = None):
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"""
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Validate column distributions are similar between the datasets.
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One advantage of the ES test compared to the KS test is that is does not assume a continuous distribution.
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In [1], the authors conclude that the test also has a higher power than the KS test in many examples. They
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recommend the use of the ES test for discrete samples as well as continuous samples with at least 25
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observations each, whereas AD is recommended for smaller sample sizes in the continuous case.
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:param original_data_members: A container for the training original samples and labels
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:param original_data_non_members: A container for the holdout original samples and labels
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:param synthetic_data: A container for the synthetic samples and labels
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:param categorical_features: a list of categorical features of the datasets
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:return:
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DistributionValidationResult
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"""
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try:
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member_column_distribution_diff = self._columns_different_distributions(synthetic_data,
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original_data_members,
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categorical_features)
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non_member_column_distribution_diff = self._columns_different_distributions(synthetic_data,
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original_data_non_members,
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categorical_features)
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except (ValueError, np.linalg.LinAlgError) as e:
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print("Failed to validate distributions", e)
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return DistributionValidationResult(distributions_validated=True,
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distributions_valid=False,
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member_column_distribution_diff=[],
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non_member_column_distribution_diff=[])
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if not member_column_distribution_diff and not non_member_column_distribution_diff:
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return DistributionValidationResult(distributions_validated=True,
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distributions_valid=True,
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member_column_distribution_diff=[],
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non_member_column_distribution_diff=[])
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return DistributionValidationResult(distributions_validated=True,
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distributions_valid=False,
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member_column_distribution_diff=member_column_distribution_diff,
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non_member_column_distribution_diff=non_member_column_distribution_diff)
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