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243 lines
8.6 KiB
243 lines
8.6 KiB
# MIPLearn: Extensible Framework for Learning-Enhanced Mixed-Integer Optimization
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# Copyright (C) 2020-2021, UChicago Argonne, LLC. All rights reserved.
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# Released under the modified BSD license. See COPYING.md for more details.
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import logging
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from typing import (
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Dict,
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List,
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Hashable,
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Any,
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TYPE_CHECKING,
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Tuple,
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Optional,
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)
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import numpy as np
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from overrides import overrides
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from miplearn.classifiers import Classifier
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from miplearn.classifiers.adaptive import AdaptiveClassifier
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from miplearn.classifiers.threshold import MinPrecisionThreshold, Threshold
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from miplearn.components import classifier_evaluation_dict
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from miplearn.components.component import Component
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from miplearn.features import Sample
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from miplearn.instance.base import Instance
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from miplearn.types import (
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LearningSolveStats,
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Category,
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Solution,
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)
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logger = logging.getLogger(__name__)
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if TYPE_CHECKING:
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from miplearn.solvers.learning import LearningSolver
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class PrimalSolutionComponent(Component):
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"""
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A component that predicts the optimal primal values for the binary decision
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variables.
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In exact mode, predicted primal solutions are provided to the solver as MIP
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starts. In heuristic mode, this component fixes the decision variables to their
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predicted values.
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"""
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def __init__(
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self,
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classifier: Classifier = AdaptiveClassifier(),
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mode: str = "exact",
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threshold: Threshold = MinPrecisionThreshold([0.98, 0.98]),
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) -> None:
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assert isinstance(classifier, Classifier)
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assert isinstance(threshold, Threshold)
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assert mode in ["exact", "heuristic"]
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self.mode = mode
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self.classifiers: Dict[Hashable, Classifier] = {}
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self.thresholds: Dict[Hashable, Threshold] = {}
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self.threshold_prototype = threshold
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self.classifier_prototype = classifier
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@overrides
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def before_solve_mip(
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self,
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solver: "LearningSolver",
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instance: Instance,
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model: Any,
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stats: LearningSolveStats,
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sample: Sample,
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) -> None:
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logger.info("Predicting primal solution...")
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# Do nothing if models are not trained
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if len(self.classifiers) == 0:
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logger.info("Classifiers not fitted. Skipping.")
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return
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# Predict solution and provide it to the solver
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solution = self.sample_predict(sample)
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assert solver.internal_solver is not None
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if self.mode == "heuristic":
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solver.internal_solver.fix(solution)
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else:
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solver.internal_solver.set_warm_start(solution)
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# Update statistics
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stats["Primal: Free"] = 0
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stats["Primal: Zero"] = 0
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stats["Primal: One"] = 0
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for (var_name, value) in solution.items():
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if value is None:
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stats["Primal: Free"] += 1
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else:
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if value < 0.5:
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stats["Primal: Zero"] += 1
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else:
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stats["Primal: One"] += 1
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logger.info(
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f"Predicted: free: {stats['Primal: Free']}, "
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f"zero: {stats['Primal: Zero']}, "
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f"one: {stats['Primal: One']}"
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)
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def sample_predict(self, sample: Sample) -> Solution:
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assert sample.after_load is not None
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assert sample.after_load.variables_old is not None
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# Compute y_pred
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x, _ = self.sample_xy(None, sample)
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y_pred = {}
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for category in x.keys():
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assert category in self.classifiers, (
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f"Classifier for category {category} has not been trained. "
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f"Please call component.fit before component.predict."
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)
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xc = np.array(x[category])
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proba = self.classifiers[category].predict_proba(xc)
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thr = self.thresholds[category].predict(xc)
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y_pred[category] = np.vstack(
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[
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proba[:, 0] >= thr[0],
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proba[:, 1] >= thr[1],
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]
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).T
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# Convert y_pred into solution
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solution: Solution = {v: None for v in sample.after_load.variables_old.keys()}
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category_offset: Dict[Hashable, int] = {cat: 0 for cat in x.keys()}
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for (var_name, var_features) in sample.after_load.variables_old.items():
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category = var_features.category
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if category not in category_offset:
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continue
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offset = category_offset[category]
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category_offset[category] += 1
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if y_pred[category][offset, 0]:
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solution[var_name] = 0.0
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if y_pred[category][offset, 1]:
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solution[var_name] = 1.0
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return solution
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@overrides
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def sample_xy(
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self,
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_: Optional[Instance],
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sample: Sample,
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) -> Tuple[Dict[Category, List[List[float]]], Dict[Category, List[List[float]]]]:
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x: Dict = {}
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y: Dict = {}
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assert sample.after_load is not None
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assert sample.after_load.instance is not None
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assert sample.after_load.variables_old is not None
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for (var_name, var) in sample.after_load.variables_old.items():
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# Initialize categories
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category = var.category
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if category is None:
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continue
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if category not in x.keys():
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x[category] = []
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y[category] = []
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# Features
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features = list(sample.after_load.instance.to_list())
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features.extend(sample.after_load.variables_old[var_name].to_list())
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if sample.after_lp is not None:
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assert sample.after_lp.variables_old is not None
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features.extend(sample.after_lp.variables_old[var_name].to_list())
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x[category].append(features)
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# Labels
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if sample.after_mip is not None:
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assert sample.after_mip.variables_old is not None
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assert sample.after_mip.variables_old[var_name] is not None
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opt_value = sample.after_mip.variables_old[var_name].value
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assert opt_value is not None
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assert 0.0 - 1e-5 <= opt_value <= 1.0 + 1e-5, (
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f"Variable {var_name} has non-binary value {opt_value} in the "
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"optimal solution. Predicting values of non-binary "
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"variables is not currently supported. Please set its "
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"category to None."
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)
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y[category].append([opt_value < 0.5, opt_value >= 0.5])
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return x, y
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@overrides
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def sample_evaluate(
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self,
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_: Optional[Instance],
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sample: Sample,
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) -> Dict[Hashable, Dict[str, float]]:
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assert sample.after_mip is not None
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assert sample.after_mip.variables_old is not None
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solution_actual = sample.after_mip.variables_old
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solution_pred = self.sample_predict(sample)
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vars_all, vars_one, vars_zero = set(), set(), set()
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pred_one_positive, pred_zero_positive = set(), set()
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for (var_name, var) in solution_actual.items():
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assert var.value is not None
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value_actual = var.value
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vars_all.add(var_name)
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if value_actual > 0.5:
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vars_one.add(var_name)
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else:
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vars_zero.add(var_name)
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value_pred = solution_pred[var_name]
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if value_pred is not None:
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if value_pred > 0.5:
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pred_one_positive.add(var_name)
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else:
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pred_zero_positive.add(var_name)
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pred_one_negative = vars_all - pred_one_positive
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pred_zero_negative = vars_all - pred_zero_positive
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return {
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0: classifier_evaluation_dict(
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tp=len(pred_zero_positive & vars_zero),
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tn=len(pred_zero_negative & vars_one),
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fp=len(pred_zero_positive & vars_one),
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fn=len(pred_zero_negative & vars_zero),
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),
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1: classifier_evaluation_dict(
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tp=len(pred_one_positive & vars_one),
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tn=len(pred_one_negative & vars_zero),
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fp=len(pred_one_positive & vars_zero),
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fn=len(pred_one_negative & vars_one),
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),
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}
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@overrides
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def fit_xy(
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self,
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x: Dict[Hashable, np.ndarray],
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y: Dict[Hashable, np.ndarray],
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) -> None:
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for category in x.keys():
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clf = self.classifier_prototype.clone()
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thr = self.threshold_prototype.clone()
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clf.fit(x[category], y[category])
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thr.fit(clf, x[category], y[category])
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self.classifiers[category] = clf
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self.thresholds[category] = thr
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