Multi-class Classification Metrics

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import numpy as np
from sklearn.metrics import precision_recall_fscore_support
from typing import Tuple, List
 
def compute_macro_metrics(
    y_true: np.ndarray, 
    y_pred: np.ndarray
) -> Tuple[float, float, float]:
    """
    Compute macro-averaged precision, recall, and F1 score.
    
    Macro averaging gives equal weight to each class, regardless of
    the number of samples in that class. This is particularly useful
    when class balance in the test set doesn't reflect production
    importance, or when minority class performance matters equally.
    
    Parameters
    ----------
    y_true : array-like of shape (n_samples,)
        Ground truth class labels
    y_pred : array-like of shape (n_samples,)
        Predicted class labels
        
    Returns
    -------
    macro_precision : float
        Macro-averaged precision
    macro_recall : float
        Macro-averaged recall
    macro_f1 : float
        Macro-averaged F1 score
        
    Mathematical Foundation
    -----------------------
    For K classes:
        Macro-M = (1/K) * sum(M_i for i in range(K))
    
    where M_i is the metric computed for class i.
    """
    precision, recall, f1, _ = precision_recall_fscore_support(
        y_true, y_pred, average='macro', zero_division=0
    )
    return precision, recall, f1
 
 
def compute_macro_metrics_manual(
    y_true: np.ndarray, 
    y_pred: np.ndarray
) -> Tuple[float, float, float, dict]:
    """
    Manual implementation of macro averaging for educational purposes.
    
    This function explicitly shows the per-class computation and averaging
    process, making the mathematical structure transparent.
    """
    classes = np.unique(np.concatenate([y_true, y_pred]))
    n_classes = len(classes)
    
    per_class_metrics = {}
    
    for cls in classes:
        # Binary mask for current class
        true_positive = np.sum((y_pred == cls) & (y_true == cls))
        false_positive = np.sum((y_pred == cls) & (y_true != cls))
        false_negative = np.sum((y_pred != cls) & (y_true == cls))
        
        # Compute per-class metrics with zero division handling
        precision = true_positive / (true_positive + false_positive) \
                    if (true_positive + false_positive) > 0 else 0.0
        recall = true_positive / (true_positive + false_negative) \
                 if (true_positive + false_negative) > 0 else 0.0
        f1 = 2 * precision * recall / (precision + recall) \
             if (precision + recall) > 0 else 0.0
        
        per_class_metrics[cls] = {
            'precision': precision,
            'recall': recall,
            'f1': f1,
            'support': np.sum(y_true == cls)
        }
    
    # Simple arithmetic mean across classes
    macro_precision = np.mean([m['precision'] for m in per_class_metrics.values()])
    macro_recall = np.mean([m['recall'] for m in per_class_metrics.values()])
    macro_f1 = np.mean([m['f1'] for m in per_class_metrics.values()])
    
    return macro_precision, macro_recall, macro_f1, per_class_metrics
 
 
# Example: Demonstrating macro averaging
def demonstrate_macro_averaging():
    """
    Demonstration showing how macro averaging handles imbalanced data.
    """
    # Simulated predictions: highly imbalanced classes
    # Class 0: 900 samples, Class 1: 80 samples, Class 2: 20 samples
    np.random.seed(42)
    
    # Ground truth
    y_true = np.array(
        [0] * 900 + [1] * 80 + [2] * 20
    )
    
    # Predictions: model performs well on majority, poorly on minority
    y_pred = np.array(
        [0] * 850 + [1] * 30 + [2] * 20 +  # Class 0: 850/900 correct
        [1] * 50 + [0] * 20 + [2] * 10 +   # Class 1: 50/80 correct  
        [2] * 5 + [0] * 10 + [1] * 5       # Class 2: 5/20 correct
    )
    
    # Compute metrics
    macro_p, macro_r, macro_f1, per_class = compute_macro_metrics_manual(
        y_true, y_pred
    )
    
    print("Per-class metrics:")
    print("-" * 60)
    for cls, metrics in per_class.items():
        print(f"Class {cls}: P={metrics['precision']:.3f}, "
              f"R={metrics['recall']:.3f}, F1={metrics['f1']:.3f}, "
              f"Support={metrics['support']}")
    print("-" * 60)
    print(f"Macro-averaged: P={macro_p:.3f}, R={macro_r:.3f}, F1={macro_f1:.3f}")
    
    return per_class
 
if __name__ == "__main__":
    demonstrate_macro_averaging()

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import numpy as np
from sklearn.metrics import precision_recall_fscore_support, accuracy_score
from typing import Tuple, Dict
 
def compute_micro_metrics(
    y_true: np.ndarray, 
    y_pred: np.ndarray
) -> Tuple[float, float, float]:
    """
    Compute micro-averaged precision, recall, and F1 score.
    
    Micro averaging pools all samples together, treating each instance
    equally regardless of class. This gives a global measure of model
    performance weighted by class frequency.
    
    In single-label multi-class classification:
        Micro-Precision = Micro-Recall = Micro-F1 = Accuracy
    
    Parameters
    ----------
    y_true : array-like of shape (n_samples,)
        Ground truth class labels
    y_pred : array-like of shape (n_samples,)
        Predicted class labels
        
    Returns
    -------
    micro_precision : float
        Micro-averaged precision
    micro_recall : float  
        Micro-averaged recall
    micro_f1 : float
        Micro-averaged F1 score
    """
    precision, recall, f1, _ = precision_recall_fscore_support(
        y_true, y_pred, average='micro', zero_division=0
    )
    return precision, recall, f1
 
 
def compute_micro_metrics_manual(
    y_true: np.ndarray, 
    y_pred: np.ndarray
) -> Tuple[float, float, float, Dict]:
    """
    Manual implementation of micro averaging for educational purposes.
    
    This function explicitly shows the pooling of counts across classes,
    demonstrating why micro metrics are dominated by majority classes.
    """
    classes = np.unique(np.concatenate([y_true, y_pred]))
    
    # Aggregate counts across all classes
    total_tp = 0
    total_fp = 0
    total_fn = 0
    
    class_details = {}
    
    for cls in classes:
        tp = np.sum((y_pred == cls) & (y_true == cls))
        fp = np.sum((y_pred == cls) & (y_true != cls))
        fn = np.sum((y_pred != cls) & (y_true == cls))
        
        total_tp += tp
        total_fp += fp
        total_fn += fn
        
        class_details[cls] = {'tp': tp, 'fp': fp, 'fn': fn}
    
    # Compute metrics from aggregated counts
    micro_precision = total_tp / (total_tp + total_fp) \
                      if (total_tp + total_fp) > 0 else 0.0
    micro_recall = total_tp / (total_tp + total_fn) \
                   if (total_tp + total_fn) > 0 else 0.0
    micro_f1 = 2 * micro_precision * micro_recall / \
               (micro_precision + micro_recall) \
               if (micro_precision + micro_recall) > 0 else 0.0
    
    aggregated = {
        'total_tp': total_tp,
        'total_fp': total_fp, 
        'total_fn': total_fn,
        'per_class': class_details
    }
    
    return micro_precision, micro_recall, micro_f1, aggregated
 
 
def demonstrate_micro_accuracy_equivalence():
    """
    Demonstrate that micro-F1 equals accuracy in single-label classification.
    """
    np.random.seed(42)
    
    # Generate random multi-class predictions
    n_samples = 1000
    n_classes = 5
    
    y_true = np.random.randint(0, n_classes, n_samples)
    y_pred = y_true.copy()
    # Introduce some errors
    error_idx = np.random.choice(n_samples, 200, replace=False)
    y_pred[error_idx] = np.random.randint(0, n_classes, len(error_idx))
    
    # Compute metrics
    accuracy = accuracy_score(y_true, y_pred)
    micro_p, micro_r, micro_f1, _ = compute_micro_metrics_manual(y_true, y_pred)
    
    print("Demonstrating Micro-F1 = Accuracy equivalence:")
    print("-" * 50)
    print(f"Accuracy:         {accuracy:.6f}")
    print(f"Micro-Precision:  {micro_p:.6f}")
    print(f"Micro-Recall:     {micro_r:.6f}")
    print(f"Micro-F1:         {micro_f1:.6f}")
    print("-" * 50)
    print(f"Difference (Micro-F1 - Accuracy): {abs(micro_f1 - accuracy):.10f}")
    
    return accuracy, micro_f1
 
 
def show_majority_class_dominance():
    """
    Illustrate how micro averaging is dominated by majority classes.
    """
    # Extreme imbalance: 950 samples from class 0, 25 each from classes 1 and 2
    y_true = np.array([0] * 950 + [1] * 25 + [2] * 25)
    
    # Model: perfect on class 0, terrible on minority classes
    y_pred = np.array(
        [0] * 950 +      # Class 0: 100% correct
        [0] * 25 +       # Class 1: 0% correct (all predicted as 0)
        [0] * 25         # Class 2: 0% correct (all predicted as 0)
    )
    
    # Compute both averaging methods
    micro_p, micro_r, micro_f1, _ = compute_micro_metrics_manual(y_true, y_pred)
    
    from compute_macro_metrics_manual import compute_macro_metrics_manual
    macro_p, macro_r, macro_f1, per_class = compute_macro_metrics_manual(y_true, y_pred)
    
    print("Majority Class Dominance in Micro Averaging:")
    print("=" * 60)
    print("Scenario: 95% class 0, 2.5% class 1, 2.5% class 2")
    print("Model: Perfect on class 0, completely fails on classes 1 and 2")
    print("-" * 60)
    print(f"Micro-averaged metrics (dominated by class 0):")
    print(f"  Precision: {micro_p:.3f}")
    print(f"  Recall:    {micro_r:.3f}")
    print(f"  F1:        {micro_f1:.3f}")
    print("-" * 60)
    print(f"Macro-averaged metrics (equal weight to all classes):")
    print(f"  Precision: {macro_p:.3f}")
    print(f"  Recall:    {macro_r:.3f}")
    print(f"  F1:        {macro_f1:.3f}")
    print("-" * 60)
    print("Observation: Micro shows 0.95 F1 (looks great!)")
    print("             Macro shows 0.32 F1 (reveals minority class failure)")
 
if __name__ == "__main__":
    demonstrate_micro_accuracy_equivalence()

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import numpy as np
import matplotlib.pyplot as plt
from sklearn.metrics import precision_recall_fscore_support
 
def analyze_metric_divergence(
    max_imbalance_ratio: int = 100,
    majority_performance: float = 0.95,
    minority_performance: float = 0.50,
    n_minority_samples: int = 100
) -> dict:
    """
    Analyze how micro and macro metrics diverge as class imbalance increases.
    
    This function systematically varies the imbalance ratio while keeping
    per-class performance constant, showing how micro averaging becomes
    increasingly insensitive to minority class failures.
    
    Parameters
    ----------
    max_imbalance_ratio : int
        Maximum ratio of majority to minority class samples
    majority_performance : float
        Accuracy on majority class (held constant)
    minority_performance : float
        Accuracy on minority class (held constant)
    n_minority_samples : int
        Fixed number of minority class samples
        
    Returns
    -------
    results : dict
        Contains imbalance ratios and corresponding metric values
    """
    imbalance_ratios = list(range(1, max_imbalance_ratio + 1, 5))
    
    micro_f1_scores = []
    macro_f1_scores = []
    
    for ratio in imbalance_ratios:
        n_majority = n_minority_samples * ratio
        
        # Generate ground truth
        y_true = np.array([0] * n_majority + [1] * n_minority_samples)
        
        # Generate predictions with fixed per-class performance
        n_correct_majority = int(n_majority * majority_performance)
        n_correct_minority = int(n_minority_samples * minority_performance)
        
        y_pred_majority = np.array(
            [0] * n_correct_majority + [1] * (n_majority - n_correct_majority)
        )
        y_pred_minority = np.array(
            [1] * n_correct_minority + [0] * (n_minority_samples - n_correct_minority)
        )
        y_pred = np.concatenate([y_pred_majority, y_pred_minority])
        
        # Compute metrics
        _, _, micro_f1, _ = precision_recall_fscore_support(
            y_true, y_pred, average='micro', zero_division=0
        )
        _, _, macro_f1, _ = precision_recall_fscore_support(
            y_true, y_pred, average='macro', zero_division=0
        )
        
        micro_f1_scores.append(micro_f1)
        macro_f1_scores.append(macro_f1)
    
    results = {
        'imbalance_ratios': imbalance_ratios,
        'micro_f1': micro_f1_scores,
        'macro_f1': macro_f1_scores,
        'divergence': [m - M for m, M in zip(micro_f1_scores, macro_f1_scores)]
    }
    
    return results
 
 
def visualize_divergence(results: dict):
    """
    Visualize the divergence between micro and macro averaging.
    """
    fig, axes = plt.subplots(1, 2, figsize=(14, 5))
    
    # Plot 1: Metric values
    ax1 = axes[0]
    ax1.plot(results['imbalance_ratios'], results['micro_f1'], 
             'b-', linewidth=2, label='Micro F1')
    ax1.plot(results['imbalance_ratios'], results['macro_f1'], 
             'r-', linewidth=2, label='Macro F1')
    ax1.set_xlabel('Imbalance Ratio (Majority/Minority)', fontsize=12)
    ax1.set_ylabel('F1 Score', fontsize=12)
    ax1.set_title('Metric Values vs Class Imbalance', fontsize=14)
    ax1.legend()
    ax1.grid(True, alpha=0.3)
    ax1.set_ylim(0, 1)
    
    # Plot 2: Divergence
    ax2 = axes[1]
    ax2.fill_between(results['imbalance_ratios'], 0, results['divergence'],
                     alpha=0.3, color='purple')
    ax2.plot(results['imbalance_ratios'], results['divergence'], 
             'purple', linewidth=2)
    ax2.set_xlabel('Imbalance Ratio (Majority/Minority)', fontsize=12)
    ax2.set_ylabel('Micro F1 - Macro F1', fontsize=12)
    ax2.set_title('Divergence Between Averaging Methods', fontsize=14)
    ax2.grid(True, alpha=0.3)
    
    plt.tight_layout()
    plt.savefig('metric_divergence.png', dpi=150, bbox_inches='tight')
    plt.show()
    
    return fig
 
 
if __name__ == "__main__":
    results = analyze_metric_divergence(
        max_imbalance_ratio=100,
        majority_performance=0.95,
        minority_performance=0.50
    )
    
    print("Divergence Analysis Results:")
    print("-" * 50)
    for ratio, micro, macro in zip(
        results['imbalance_ratios'][:10],
        results['micro_f1'][:10],
        results['macro_f1'][:10]
    ):
        print(f"Ratio {ratio:3d}:1 | Micro: {micro:.3f} | Macro: {macro:.3f} | "
              f"Gap: {micro - macro:.3f}")
    
    visualize_divergence(results)

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import numpy as np
from typing import List, Tuple
 
def decompose_micro_macro_gap(
    per_class_metrics: List[float],
    per_class_weights: List[float]
) -> Tuple[float, float, float, np.ndarray]:
    """
    Decompose the gap between micro and macro averaging.
    
    The gap can be written as:
        Micro - Macro = sum_i (w_i - 1/K) * M_i
    
    This function analyzes the contribution of each class to the gap.
    
    Parameters
    ----------
    per_class_metrics : list of float
        Metric value for each class (e.g., precision or F1)
    per_class_weights : list of float
        Implicit weight of each class in micro averaging
        
    Returns
    -------
    micro : float
        Micro-averaged metric
    macro : float
        Macro-averaged metric
    gap : float
        Difference (micro - macro)
    contributions : ndarray
        Per-class contribution to the gap
    """
    K = len(per_class_metrics)
    M = np.array(per_class_metrics)
    W = np.array(per_class_weights)
    
    # Normalize weights to sum to 1
    W = W / W.sum()
    
    # Compute averages
    micro = np.sum(W * M)
    macro = np.mean(M)
    
    # Decompose gap
    weight_deviations = W - 1/K
    contributions = weight_deviations * M
    gap = np.sum(contributions)
    
    return micro, macro, gap, contributions
 
 
def analyze_gap_contributors():
    """
    Illustrate which classes contribute to micro-macro divergence.
    """
    # Example: 5 classes with varying sizes and performances
    per_class_f1 = [0.95, 0.88, 0.72, 0.55, 0.40]  # Performance
    per_class_size = [10000, 5000, 2000, 500, 100]  # Class sizes
    
    # Weights are proportional to size (simplified for F1)
    weights = np.array(per_class_size, dtype=float)
    
    micro, macro, gap, contributions = decompose_micro_macro_gap(
        per_class_f1, weights
    )
    
    print("Gap Decomposition Analysis:")
    print("=" * 65)
    print(f"{'Class':<8} {'Size':<10} {'Weight':<10} {'F1':<8} {'Contribution':<12}")
    print("-" * 65)
    
    norm_weights = weights / weights.sum()
    for i, (f1, size, w, c) in enumerate(zip(
        per_class_f1, per_class_size, norm_weights, contributions
    )):
        print(f"{i:<8} {size:<10} {w:<10.4f} {f1:<8.3f} {c:+.4f}")
    
    print("-" * 65)
    print(f"Micro F1: {micro:.4f}")
    print(f"Macro F1: {macro:.4f}")
    print(f"Gap (Micro - Macro): {gap:+.4f}")
    print("-" * 65)
    print("\nInterpretation:")
    print(f"  - Large positive contributions from classes {np.argmax(contributions)}")
    print(f"  - Large negative contributions from classes {np.argmin(contributions)}")
    print(f"  - Micro > Macro because large classes have high performance")
 
 
def prove_micro_bounds():
    """
    Demonstrate that micro averaging is bounded by weighted extremes.
    """
    # For any set of per-class metrics and weights
    np.random.seed(42)
    
    n_trials = 1000
    bounds_satisfied = 0
    
    for _ in range(n_trials):
        K = np.random.randint(3, 10)
        weights = np.random.dirichlet(np.ones(K))
        metrics = np.random.uniform(0, 1, K)
        
        micro = np.sum(weights * metrics)
        
        # Check bounds
        lower_bound = np.min(metrics)
        upper_bound = np.max(metrics)
        
        if lower_bound <= micro <= upper_bound:
            bounds_satisfied += 1
    
    print(f"\nBounds verification ({n_trials} trials):")
    print(f"  Micro within [min(M_i), max(M_i)]: {bounds_satisfied}/{n_trials} "
          f"({100*bounds_satisfied/n_trials:.1f}%)")
    
    return bounds_satisfied == n_trials
 
if __name__ == "__main__":
    analyze_gap_contributors()
    prove_micro_bounds()

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import numpy as np
from sklearn.metrics import classification_report, precision_recall_fscore_support
from typing import Dict, Any, Optional
import json
 
class MultiClassEvaluator:
    """
    Production-grade multi-class evaluation with comprehensive averaging.
    
    This class provides a complete evaluation framework that computes
    all averaging methods, handles edge cases, and produces stakeholder-
    friendly reports.
    """
    
    def __init__(
        self,
        class_names: Optional[Dict[int, str]] = None,
        zero_division: float = 0.0
    ):
        """
        Initialize the evaluator.
        
        Parameters
        ----------
        class_names : dict, optional
            Mapping from class index to human-readable name
        zero_division : float
            Value to return when a metric is undefined (division by zero)
        """
        self.class_names = class_names or {}
        self.zero_division = zero_division
        
    def evaluate(
        self,
        y_true: np.ndarray,
        y_pred: np.ndarray,
        y_prob: Optional[np.ndarray] = None
    ) -> Dict[str, Any]:
        """
        Perform comprehensive multi-class evaluation.
        
        Returns metrics at all levels: per-class, micro, macro, and weighted.
        
        Parameters
        ----------
        y_true : ndarray
            Ground truth labels
        y_pred : ndarray
            Predicted labels
        y_prob : ndarray, optional
            Predicted probabilities for each class
            
        Returns
        -------
        report : dict
            Complete evaluation report
        """
        classes = np.unique(np.concatenate([y_true, y_pred]))
        n_classes = len(classes)
        n_samples = len(y_true)
        
        # Per-class metrics
        per_class = {}
        for cls in classes:
            name = self.class_names.get(cls, f"Class_{cls}")
            
            tp = np.sum((y_pred == cls) & (y_true == cls))
            fp = np.sum((y_pred == cls) & (y_true != cls))
            fn = np.sum((y_pred != cls) & (y_true == cls))
            support = np.sum(y_true == cls)
            
            precision = self._safe_divide(tp, tp + fp)
            recall = self._safe_divide(tp, tp + fn)
            f1 = self._safe_divide(2 * precision * recall, precision + recall)
            
            per_class[name] = {
                'precision': precision,
                'recall': recall,
                'f1': f1,
                'support': int(support),
                'true_positives': int(tp),
                'false_positives': int(fp),
                'false_negatives': int(fn)
            }
        
        # Aggregated metrics
        micro_p, micro_r, micro_f1, _ = precision_recall_fscore_support(
            y_true, y_pred, average='micro', zero_division=self.zero_division
        )
        macro_p, macro_r, macro_f1, _ = precision_recall_fscore_support(
            y_true, y_pred, average='macro', zero_division=self.zero_division
        )
        weighted_p, weighted_r, weighted_f1, _ = precision_recall_fscore_support(
            y_true, y_pred, average='weighted', zero_division=self.zero_division
        )
        
        accuracy = np.mean(y_true == y_pred)
        
        # Compute gap as diagnostic
        micro_macro_gap = micro_f1 - macro_f1
        
        report = {
            'summary': {
                'n_samples': n_samples,
                'n_classes': n_classes,
                'accuracy': float(accuracy),
                'micro_macro_gap': float(micro_macro_gap),
                'class_balance': self._compute_balance_metrics(y_true, classes)
            },
            'micro': {
                'precision': float(micro_p),
                'recall': float(micro_r),
                'f1': float(micro_f1)
            },
            'macro': {
                'precision': float(macro_p),
                'recall': float(macro_r),
                'f1': float(macro_f1)
            },
            'weighted': {
                'precision': float(weighted_p),
                'recall': float(weighted_r),
                'f1': float(weighted_f1)
            },
            'per_class': per_class
        }
        
        return report
    
    def _safe_divide(self, numerator: float, denominator: float) -> float:
        """Safe division with zero handling."""
        return numerator / denominator if denominator > 0 else self.zero_division
    
    def _compute_balance_metrics(
        self,
        y_true: np.ndarray,
        classes: np.ndarray
    ) -> Dict[str, float]:
        """Compute class balance statistics."""
        counts = [np.sum(y_true == c) for c in classes]
        total = len(y_true)
        
        imbalance_ratio = max(counts) / min(counts) if min(counts) > 0 else float('inf')
        
        # Gini coefficient of class distribution
        proportions = np.array(counts) / total
        gini = 1 - np.sum(proportions ** 2)
        
        return {
            'imbalance_ratio': float(imbalance_ratio),
            'normalized_entropy': float(self._normalized_entropy(proportions)),
            'gini_coefficient': float(gini)
        }
    
    def _normalized_entropy(self, proportions: np.ndarray) -> float:
        """Compute normalized entropy of class distribution."""
        proportions = proportions[proportions > 0]  # Avoid log(0)
        entropy = -np.sum(proportions * np.log(proportions))
        max_entropy = np.log(len(proportions))
        return entropy / max_entropy if max_entropy > 0 else 0.0
    
    def format_report(self, report: Dict[str, Any]) -> str:
        """Format report as human-readable string."""
        lines = []
        lines.append("=" * 70)
        lines.append("MULTI-CLASS CLASSIFICATION REPORT")
        lines.append("=" * 70)
        
        # Summary
        s = report['summary']
        lines.append(f"\nSamples: {s['n_samples']:,} | Classes: {s['n_classes']}")
        lines.append(f"Accuracy: {s['accuracy']:.4f}")
        lines.append(f"Micro-Macro Gap: {s['micro_macro_gap']:+.4f}")
        lines.append(f"Imbalance Ratio: {s['class_balance']['imbalance_ratio']:.2f}")
        
        # Aggregated metrics
        lines.append("\n" + "-" * 70)
        lines.append(f"{'Averaging':<12} {'Precision':<12} {'Recall':<12} {'F1':<12}")
        lines.append("-" * 70)
        
        for avg in ['micro', 'macro', 'weighted']:
            m = report[avg]
            lines.append(f"{avg.capitalize():<12} {m['precision']:<12.4f} "
                        f"{m['recall']:<12.4f} {m['f1']:<12.4f}")
        
        # Per-class
        lines.append("\n" + "-" * 70)
        lines.append(f"{'Class':<20} {'P':<8} {'R':<8} {'F1':<8} {'Support':<10}")
        lines.append("-" * 70)
        
        for name, m in report['per_class'].items():
            lines.append(f"{name:<20} {m['precision']:<8.4f} {m['recall']:<8.4f} "
                        f"{m['f1']:<8.4f} {m['support']:<10}")
        
        lines.append("=" * 70)
        
        return "\n".join(lines)
 
 
# Example usage
def demonstrate_evaluator():
    np.random.seed(42)
    
    # Simulate imbalanced multi-class problem
    y_true = np.concatenate([
        np.zeros(800),
        np.ones(150),
        np.full(50, 2)
    ]).astype(int)
    
    y_pred = y_true.copy()
    # Add errors
    y_pred[:80] = 1  # Some class 0 predicted as 1
    y_pred[800:820] = 0  # Some class 1 predicted as 0
    y_pred[950:] = 1  # All class 2 predicted as 1
    
    evaluator = MultiClassEvaluator(
        class_names={0: 'Negative', 1: 'Neutral', 2: 'Positive'}
    )
    
    report = evaluator.evaluate(y_true, y_pred)
    print(evaluator.format_report(report))
    
    return report
 
if __name__ == "__main__":
    demonstrate_evaluator()