AbdCTBench / code /model /flexible_multitask_head.py
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training and testing code for AbdCTBench
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"""
Flexible Multi-Task Head and Loss Function
Adapts to any biomarker configuration without hardcoded assumptions
"""
import torch
import torch.nn as nn
import torch.nn.functional as F
import numpy as np
from typing import Dict, List, Tuple, Any, Union, Optional
import logging
from config.biomarker_config import FlexibleBiomarkerConfig, TensorLayout
from .single_target_strategies import (
SingleTargetStrategy,
create_feature_extractor,
get_strategy_from_name
)
logger = logging.getLogger(__name__)
class FlexibleMultiTaskHead(nn.Module):
"""Flexible multi-task head that adapts to biomarker configuration"""
def __init__(
self,
input_dim: int,
biomarker_config: FlexibleBiomarkerConfig,
dropout: float = 0.1,
single_target_strategy: Optional[Union[str, SingleTargetStrategy]] = None,
target_feature_dim: Optional[int] = None
):
super().__init__()
self.biomarker_config = biomarker_config
self.tensor_layout = biomarker_config.get_tensor_layout()
# Handle single-target strategy
self.single_target_strategy = None
self.feature_extractor = None
self.target_feature_dim = target_feature_dim
if single_target_strategy is not None:
if isinstance(single_target_strategy, str):
self.single_target_strategy = get_strategy_from_name(single_target_strategy)
else:
self.single_target_strategy = single_target_strategy
# Create appropriate feature extractor with target feature dimension
feature_dim = target_feature_dim if target_feature_dim is not None else input_dim
self.feature_extractor = create_feature_extractor(
self.single_target_strategy,
input_dim,
feature_dim=feature_dim,
dropout=dropout
)
# Use feature extractor output dimension
processed_input_dim = self.feature_extractor.output_dim
else:
# Default behavior - use original input dimension
processed_input_dim = input_dim
# Shared feature processing (only if no single-target strategy is used)
if self.single_target_strategy is None:
# Use target_feature_dim if provided, otherwise use 512 as default
output_dim = target_feature_dim if target_feature_dim is not None else 512
self.shared_layers = nn.Sequential(
nn.Linear(input_dim, output_dim),
nn.ReLU(inplace=True),
nn.Dropout(dropout),
nn.BatchNorm1d(output_dim)
)
processed_input_dim = output_dim
else:
# Skip shared layers when using single-target strategy
self.shared_layers = nn.Identity()
processed_input_dim = self.feature_extractor.output_dim
# Task-specific heads
self.task_heads = nn.ModuleDict()
# Binary classification heads (one per biomarker)
for biomarker in biomarker_config.binary_biomarkers:
self.task_heads[f"binary_{biomarker.name}"] = nn.Linear(processed_input_dim, 1)
# Multiclass classification heads
for biomarker in biomarker_config.multiclass_biomarkers:
num_classes = len(biomarker.classes)
self.task_heads[f"multiclass_{biomarker.name}"] = nn.Linear(processed_input_dim, num_classes)
# Regression heads (one per biomarker)
for biomarker in biomarker_config.continuous_biomarkers:
self.task_heads[f"continuous_{biomarker.name}"] = nn.Linear(processed_input_dim, 1)
def forward(self, x):
"""
Forward pass
Args:
x: Input features [batch_size, input_dim] or [batch_size, C, H, W] for spatial features
Returns:
Concatenated outputs [batch_size, total_output_size]
"""
# Apply single-target strategy feature extraction if specified
if self.single_target_strategy is not None and self.feature_extractor is not None:
shared_features = self.feature_extractor(x)
else:
shared_features = self.shared_layers(x)
outputs = []
# Binary outputs
for biomarker in self.biomarker_config.binary_biomarkers:
head_name = f"binary_{biomarker.name}"
binary_out = self.task_heads[head_name](shared_features) # [B, 1]
outputs.append(binary_out)
# Multiclass outputs
for biomarker in self.biomarker_config.multiclass_biomarkers:
head_name = f"multiclass_{biomarker.name}"
multiclass_out = self.task_heads[head_name](shared_features) # [B, num_classes]
outputs.append(multiclass_out)
# Regression outputs
for biomarker in self.biomarker_config.continuous_biomarkers:
head_name = f"continuous_{biomarker.name}"
regression_out = self.task_heads[head_name](shared_features) # [B, 1]
outputs.append(regression_out)
# Concatenate all outputs
return torch.cat(outputs, dim=1)
class LinearProbeMultiTaskHead(nn.Module):
"""
True linear probe head - direct mapping from backbone features to task outputs
No shared layers, minimal parameters, maximum interpretability
"""
def __init__(
self,
input_dim: int,
biomarker_config: FlexibleBiomarkerConfig,
dropout: float = 0.0,
single_target_strategy: Optional[Union[str, SingleTargetStrategy]] = None,
target_feature_dim: Optional[int] = None
):
super().__init__()
self.biomarker_config = biomarker_config
self.tensor_layout = biomarker_config.get_tensor_layout()
# Handle single-target strategy
self.single_target_strategy = None
self.feature_extractor = None
self.target_feature_dim = target_feature_dim
if single_target_strategy is not None:
if isinstance(single_target_strategy, str):
self.single_target_strategy = get_strategy_from_name(single_target_strategy)
else:
self.single_target_strategy = single_target_strategy
# Create appropriate feature extractor with target feature dimension
feature_dim = target_feature_dim if target_feature_dim is not None else input_dim
self.feature_extractor = create_feature_extractor(
self.single_target_strategy,
input_dim,
feature_dim=feature_dim,
dropout=0.0 # No dropout for linear probe
)
# Use feature extractor output dimension
processed_input_dim = self.feature_extractor.output_dim
else:
# Default behavior - use original input dimension
processed_input_dim = input_dim
# Optional minimal dropout (usually 0.0 for true linear probe)
self.dropout = nn.Dropout(dropout) if dropout > 0 else nn.Identity()
# Direct task-specific linear layers (no shared processing)
self.task_heads = nn.ModuleDict()
# Binary classification heads - direct from backbone
for biomarker in biomarker_config.binary_biomarkers:
self.task_heads[f"binary_{biomarker.name}"] = nn.Linear(processed_input_dim, 1)
# Multiclass classification heads - direct from backbone
for biomarker in biomarker_config.multiclass_biomarkers:
num_classes = len(biomarker.classes)
self.task_heads[f"multiclass_{biomarker.name}"] = nn.Linear(processed_input_dim, num_classes)
# Regression heads - direct from backbone
for biomarker in biomarker_config.continuous_biomarkers:
self.task_heads[f"continuous_{biomarker.name}"] = nn.Linear(processed_input_dim, 1)
# Initialize weights for better convergence
self._initialize_weights()
def _initialize_weights(self):
"""Initialize linear layer weights for stable training"""
for name, module in self.task_heads.items():
if isinstance(module, nn.Linear):
# Xavier/Glorot initialization for linear layers
nn.init.xavier_uniform_(module.weight)
nn.init.zeros_(module.bias)
def forward(self, x):
"""
Direct forward pass - no shared processing
Args:
x: Backbone features [batch_size, input_dim] or [batch_size, C, H, W] for spatial features
Returns:
Concatenated outputs [batch_size, total_output_size]
"""
# Apply single-target strategy feature extraction if specified
if self.single_target_strategy is not None and self.feature_extractor is not None:
features = self.feature_extractor(x)
else:
# Optional dropout on backbone features (usually disabled)
features = self.dropout(x) # [batch_size, input_dim]
outputs = []
# Binary outputs - direct linear transformation
for biomarker in self.biomarker_config.binary_biomarkers:
head_name = f"binary_{biomarker.name}"
binary_out = self.task_heads[head_name](features) # [B, 1]
outputs.append(binary_out)
# Multiclass outputs - direct linear transformation
for biomarker in self.biomarker_config.multiclass_biomarkers:
head_name = f"multiclass_{biomarker.name}"
multiclass_out = self.task_heads[head_name](features) # [B, num_classes]
outputs.append(multiclass_out)
# Regression outputs - direct linear transformation
for biomarker in self.biomarker_config.continuous_biomarkers:
head_name = f"continuous_{biomarker.name}"
regression_out = self.task_heads[head_name](features) # [B, 1]
outputs.append(regression_out)
# Concatenate all outputs
return torch.cat(outputs, dim=1) # [batch_size, total_output_size]
class FlexibleMultiTaskLoss(nn.Module):
"""Flexible multi-task loss function that adapts to biomarker configuration"""
def __init__(self, biomarker_config: FlexibleBiomarkerConfig, class_weights: Dict[str, float] = None):
super().__init__()
self.biomarker_config = biomarker_config
self.tensor_layout = biomarker_config.get_tensor_layout()
self.class_weights = class_weights or {}
# Create weighted BCE losses for binary tasks
self.binary_losses = nn.ModuleDict()
for biomarker in biomarker_config.binary_biomarkers:
weight = self.class_weights.get(biomarker.name, 1.0)
if weight != 1.0:
pos_weight = torch.tensor([weight], dtype=torch.float32)
self.binary_losses[biomarker.name] = nn.BCEWithLogitsLoss(pos_weight=pos_weight)
else:
self.binary_losses[biomarker.name] = nn.BCEWithLogitsLoss()
# Cross-entropy losses for multiclass tasks
self.multiclass_losses = nn.ModuleDict()
for biomarker in biomarker_config.multiclass_biomarkers:
self.multiclass_losses[biomarker.name] = nn.CrossEntropyLoss()
# MSE losses for regression tasks
self.regression_losses = nn.ModuleDict()
for biomarker in biomarker_config.continuous_biomarkers:
self.regression_losses[biomarker.name] = nn.MSELoss()
def forward(self, predictions: torch.Tensor, targets: torch.Tensor) -> Tuple[torch.Tensor, Dict[str, float]]:
"""
Calculate multi-task loss
Args:
predictions: [batch_size, total_output_size]
targets: [batch_size, total_output_size]
Returns:
total_loss: Combined loss
loss_dict: Dictionary with individual loss components
"""
device = predictions.device
# Move pos_weight tensors to correct device
for biomarker_name, loss_fn in self.binary_losses.items():
if hasattr(loss_fn, 'pos_weight') and loss_fn.pos_weight is not None:
loss_fn.pos_weight = loss_fn.pos_weight.to(device)
total_loss = 0.0
loss_components = {}
# Binary classification losses
binary_losses = []
for biomarker in self.biomarker_config.binary_biomarkers:
layout = self.tensor_layout[biomarker.name]
pred_slice = predictions[:, layout.start_idx:layout.end_idx].squeeze(-1) # [B]
target_slice = targets[:, layout.start_idx:layout.end_idx].squeeze(-1) # [B]
loss_fn = self.binary_losses[biomarker.name]
binary_loss = loss_fn(pred_slice, target_slice)
binary_losses.append(binary_loss)
loss_components[f'binary_{biomarker.name}'] = binary_loss.item()
if binary_losses:
avg_binary_loss = torch.mean(torch.stack(binary_losses))
total_loss += avg_binary_loss
loss_components['avg_binary_loss'] = avg_binary_loss.item()
# Multiclass classification losses
multiclass_losses = []
for biomarker in self.biomarker_config.multiclass_biomarkers:
layout = self.tensor_layout[biomarker.name]
pred_slice = predictions[:, layout.start_idx:layout.end_idx] # [B, num_classes]
target_slice = targets[:, layout.start_idx:layout.end_idx] # [B, num_classes]
# Convert one-hot targets to class indices
target_indices = torch.argmax(target_slice, dim=1) # [B]
loss_fn = self.multiclass_losses[biomarker.name]
multiclass_loss = loss_fn(pred_slice, target_indices)
multiclass_losses.append(multiclass_loss)
loss_components[f'multiclass_{biomarker.name}'] = multiclass_loss.item()
if multiclass_losses:
avg_multiclass_loss = torch.mean(torch.stack(multiclass_losses))
total_loss += avg_multiclass_loss
loss_components['avg_multiclass_loss'] = avg_multiclass_loss.item()
# Regression losses
regression_losses = []
for biomarker in self.biomarker_config.continuous_biomarkers:
layout = self.tensor_layout[biomarker.name]
pred_slice = predictions[:, layout.start_idx:layout.end_idx].squeeze(-1) # [B]
target_slice = targets[:, layout.start_idx:layout.end_idx].squeeze(-1) # [B]
loss_fn = self.regression_losses[biomarker.name]
regression_loss = loss_fn(pred_slice, target_slice)
regression_losses.append(regression_loss)
loss_components[f'regression_{biomarker.name}'] = regression_loss.item()
if regression_losses:
avg_regression_loss = torch.mean(torch.stack(regression_losses))
total_loss += avg_regression_loss
loss_components['avg_regression_loss'] = avg_regression_loss.item()
loss_components['total_loss'] = total_loss.item()
return total_loss, loss_components
class FlexibleMetricsCalculator:
"""Calculate comprehensive metrics for flexible multi-task learning"""
def __init__(self, biomarker_config: FlexibleBiomarkerConfig):
self.biomarker_config = biomarker_config
self.tensor_layout = biomarker_config.get_tensor_layout()
# Threshold optimization settings from config
validation_config = biomarker_config.validation
self.threshold_optimization = validation_config.get('threshold_optimization', False)
self.optimization_metric = validation_config.get('optimization_metric', 'f1_score')
self.per_biomarker_thresholds = validation_config.get('per_biomarker_thresholds', True)
self.threshold_range = validation_config.get('threshold_search_range', [0.1, 0.9])
self.threshold_steps = validation_config.get('threshold_search_steps', 81)
self.fallback_threshold = validation_config.get('fallback_threshold', 0.5)
# Store optimal thresholds per biomarker
self.optimal_thresholds = {}
def find_optimal_threshold(self, pred_probs: np.ndarray, true_labels: np.ndarray,
metric: str = 'f1_score') -> Tuple[float, float]:
"""
Find optimal threshold for a single biomarker based on specified metric
Args:
pred_probs: Predicted probabilities [N]
true_labels: True binary labels [N]
metric: Metric to optimize ('f1_score', 'sensitivity', 'specificity', etc.)
Returns:
best_threshold: Optimal threshold value
best_score: Best metric score achieved
"""
from sklearn.metrics import f1_score, precision_score, recall_score
# Create threshold search space
thresholds = np.linspace(self.threshold_range[0], self.threshold_range[1], self.threshold_steps)
best_threshold = self.fallback_threshold
best_score = 0.0
for threshold in thresholds:
pred_labels = (pred_probs > threshold).astype(int)
try:
if metric == 'f1_score':
score = f1_score(true_labels, pred_labels, zero_division=0.0)
elif metric == 'precision':
score = precision_score(true_labels, pred_labels, zero_division=0.0)
elif metric == 'recall' or metric == 'sensitivity':
score = recall_score(true_labels, pred_labels, zero_division=0.0)
elif metric == 'specificity':
# Specificity = TN / (TN + FP)
tn = np.sum((pred_labels == 0) & (true_labels == 0))
fp = np.sum((pred_labels == 1) & (true_labels == 0))
score = tn / (tn + fp + 1e-8)
elif metric == 'accuracy':
score = (pred_labels == true_labels).mean()
else:
# Default to f1_score
score = f1_score(true_labels, pred_labels, zero_division=0.0)
if score > best_score:
best_score = score
best_threshold = threshold
except (ValueError, ZeroDivisionError):
continue
return best_threshold, best_score
def optimize_thresholds(self, predictions: torch.Tensor, targets: torch.Tensor) -> Dict[str, float]:
"""
Find optimal thresholds for all binary biomarkers
Args:
predictions: Model predictions [batch_size, total_output_size]
targets: True targets [batch_size, total_output_size]
Returns:
Dictionary mapping biomarker names to optimal thresholds
"""
# Convert to numpy
if isinstance(predictions, torch.Tensor):
predictions = predictions.detach().cpu().numpy()
if isinstance(targets, torch.Tensor):
targets = targets.detach().cpu().numpy()
optimal_thresholds = {}
for biomarker in self.biomarker_config.binary_biomarkers:
layout = self.tensor_layout[biomarker.name]
pred_logits = predictions[:, layout.start_idx]
pred_probs = 1 / (1 + np.exp(-pred_logits)) # Sigmoid
true_labels = targets[:, layout.start_idx].astype(int)
# Skip if all labels are the same (no positive or negative examples)
if len(np.unique(true_labels)) < 2:
optimal_thresholds[biomarker.name] = self.fallback_threshold
continue
# Find optimal threshold
best_threshold, best_score = self.find_optimal_threshold(
pred_probs, true_labels, self.optimization_metric
)
optimal_thresholds[biomarker.name] = best_threshold
# Log the optimization result
logger.info(
" %s: threshold=%.3f, %s=%.3f",
biomarker.name,
best_threshold,
self.optimization_metric,
best_score,
)
return optimal_thresholds
def update_optimal_thresholds(self, predictions: torch.Tensor, targets: torch.Tensor):
"""Update optimal thresholds based on current predictions and targets"""
if self.threshold_optimization:
logger.info("Optimizing thresholds...")
self.optimal_thresholds = self.optimize_thresholds(predictions, targets)
else:
# Use fallback threshold for all biomarkers
for biomarker in self.biomarker_config.binary_biomarkers:
self.optimal_thresholds[biomarker.name] = self.fallback_threshold
def calculate_binary_metrics(self, predictions: torch.Tensor, targets: torch.Tensor,
use_optimal_thresholds: bool = True) -> Dict[str, Dict[str, float]]:
"""Calculate metrics for binary classification tasks"""
metrics = {}
# Convert to numpy
if isinstance(predictions, torch.Tensor):
predictions = predictions.detach().cpu().numpy()
if isinstance(targets, torch.Tensor):
targets = targets.detach().cpu().numpy()
for biomarker in self.biomarker_config.binary_biomarkers:
layout = self.tensor_layout[biomarker.name]
pred_logits = predictions[:, layout.start_idx]
pred_probs = 1 / (1 + np.exp(-pred_logits)) # Sigmoid
true_labels = targets[:, layout.start_idx].astype(int)
# AUROC (threshold-independent)
try:
from sklearn.metrics import roc_auc_score
auroc = roc_auc_score(true_labels, pred_probs)
except (ValueError, ImportError):
auroc = 0.0
# Get threshold for this biomarker
if use_optimal_thresholds and biomarker.name in self.optimal_thresholds:
threshold = self.optimal_thresholds[biomarker.name]
else:
threshold = self.fallback_threshold
# Predictions with threshold
pred_labels = (pred_probs > threshold).astype(int)
# Basic metrics
accuracy = (pred_labels == true_labels).mean()
# Confusion matrix components
true_positives = np.sum((pred_labels == 1) & (true_labels == 1))
true_negatives = np.sum((pred_labels == 0) & (true_labels == 0))
false_positives = np.sum((pred_labels == 1) & (true_labels == 0))
false_negatives = np.sum((pred_labels == 0) & (true_labels == 1))
# Sensitivity and Specificity
sensitivity = true_positives / (true_positives + false_negatives) if (true_positives + false_negatives) > 0 else 0.0
specificity = true_negatives / (true_negatives + false_positives) if (true_negatives + false_positives) > 0 else 0.0
# F1 Score
try:
from sklearn.metrics import f1_score
f1 = f1_score(true_labels, pred_labels, zero_division=0.0)
except ImportError:
precision = true_positives / (true_positives + false_positives) if (true_positives + false_positives) > 0 else 0.0
recall = sensitivity
f1 = 2 * (precision * recall) / (precision + recall + 1e-8)
metrics[biomarker.name] = {
'auroc': float(auroc),
'accuracy': float(accuracy),
'sensitivity': float(sensitivity),
'specificity': float(specificity),
'f1': float(f1),
'threshold': float(threshold), # Include threshold used
'true_positives': int(true_positives),
'true_negatives': int(true_negatives),
'false_positives': int(false_positives),
'false_negatives': int(false_negatives)
}
return metrics
def calculate_multiclass_metrics(self, predictions: torch.Tensor, targets: torch.Tensor) -> Dict[str, Dict[str, Any]]:
"""Calculate metrics for multiclass classification tasks"""
metrics = {}
# Convert to numpy
if isinstance(predictions, torch.Tensor):
predictions = predictions.detach().cpu().numpy()
if isinstance(targets, torch.Tensor):
targets = targets.detach().cpu().numpy()
for biomarker in self.biomarker_config.multiclass_biomarkers:
layout = self.tensor_layout[biomarker.name]
pred_logits = predictions[:, layout.start_idx:layout.end_idx]
# Numerically stable softmax
max_logits = np.max(pred_logits, axis=1, keepdims=True)
exp_logits = np.exp(pred_logits - max_logits)
pred_probs = exp_logits / (np.sum(exp_logits, axis=1, keepdims=True) + 1e-12)
target_one_hot = targets[:, layout.start_idx:layout.end_idx]
# Get predicted and true classes
pred_classes = np.argmax(pred_probs, axis=1)
true_classes = np.argmax(target_one_hot, axis=1)
# Overall accuracy
accuracy = (pred_classes == true_classes).mean()
# Multi-class AUROC
try:
from sklearn.metrics import roc_auc_score
auroc = roc_auc_score(target_one_hot, pred_probs, multi_class='ovr', average='macro')
except (ValueError, ImportError):
auroc = 0.0
metrics[biomarker.name] = {
'accuracy': float(accuracy),
'auroc': float(auroc)
}
return metrics
def calculate_regression_metrics(self, predictions: torch.Tensor, targets: torch.Tensor) -> Dict[str, Dict[str, float]]:
"""Calculate metrics for regression tasks"""
metrics = {}
# Convert to numpy
if isinstance(predictions, torch.Tensor):
predictions = predictions.detach().cpu().numpy()
if isinstance(targets, torch.Tensor):
targets = targets.detach().cpu().numpy()
for biomarker in self.biomarker_config.continuous_biomarkers:
layout = self.tensor_layout[biomarker.name]
pred_values = predictions[:, layout.start_idx]
true_values = targets[:, layout.start_idx]
# Denormalize if needed
if biomarker.normalization == "min_max":
pred_denorm = pred_values * (biomarker.max_value - biomarker.min_value) + biomarker.min_value
true_denorm = true_values * (biomarker.max_value - biomarker.min_value) + biomarker.min_value
else:
pred_denorm = pred_values
true_denorm = true_values
# Calculate metrics
mse = np.mean((pred_denorm - true_denorm) ** 2)
mae = np.mean(np.abs(pred_denorm - true_denorm))
# R² score
ss_res = np.sum((true_denorm - pred_denorm) ** 2)
ss_tot = np.sum((true_denorm - np.mean(true_denorm)) ** 2)
r2 = 1 - (ss_res / (ss_tot + 1e-8))
metrics[biomarker.name] = {
'mse': float(mse),
'mae': float(mae),
'r2': float(r2)
}
return metrics
def calculate_all_metrics(self, predictions: torch.Tensor, targets: torch.Tensor) -> Dict[str, Any]:
"""Calculate all metrics"""
all_metrics = {}
# Binary metrics
if self.biomarker_config.binary_biomarkers:
binary_metrics = self.calculate_binary_metrics(predictions, targets)
all_metrics.update(binary_metrics)
# Multiclass metrics
if self.biomarker_config.multiclass_biomarkers:
multiclass_metrics = self.calculate_multiclass_metrics(predictions, targets)
all_metrics.update(multiclass_metrics)
# Regression metrics
if self.biomarker_config.continuous_biomarkers:
regression_metrics = self.calculate_regression_metrics(predictions, targets)
all_metrics.update(regression_metrics)
# Calculate both average and median AUROC for comprehensive monitoring
auroc_values = []
for biomarker_name, metrics in all_metrics.items():
if isinstance(metrics, dict) and 'auroc' in metrics:
auroc_values.append(metrics['auroc'])
if auroc_values:
all_metrics['average_auroc'] = float(np.mean(auroc_values))
all_metrics['median_auroc'] = float(np.median(auroc_values))
else:
all_metrics['average_auroc'] = 0.0
all_metrics['median_auroc'] = 0.0
return all_metrics