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Intelligently selecting which samples to label to maximize model performance with minimal annotation
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| name | Active Learning |
| category | data-science |
| description | Intelligently selecting which samples to label to maximize model performance with minimal annotation |
I enable models to strategically select which unlabeled examples would be most informative to label next. By querying only the most valuable samples, I can achieve high performance with significantly fewer labels than random sampling. This is essential when labeling is expensive or time-consuming.
Uncertainty Sampling: Selecting examples where the model is most uncertain.
Query Strategy: The algorithm for selecting which samples to query.
Pool-Based Active Learning: Selecting from a large unlabeled pool.
Stream-Based Active Learning: Making sequential decisions as data arrives.
Batch Active Learning: Selecting multiple samples per iteration.
Diversity Sampling: Ensuring selected samples are representative.
Expected Model Change: Selecting samples that would most change the model.
Acquisition Function: The function that scores unlabeled examples.
import torch
import torch.nn as nn
import torch.nn.functional as F
import numpy as np
class UncertaintySampling:
def __init__(self, model):
self.model = model
def least_confidence(self, probs):
confidence = probs.max(dim=1)[0]
return 1 - confidence
def margin_sampling(self, probs):
sorted_probs, _ = probs.sort(dim=1, descending=True)
margin = sorted_probs[:, 0] - sorted_probs[:, 1]
return -margin
def entropy(self, probs):
return -(probs * torch.log(probs + 1e-10)).sum(dim=1)
def query(self, unlabeled_loader, method="entropy", n_samples=10):
self.model.eval()
all_scores = []
all_indices = []
with torch.no_grad():
for indices, data in unlabeled_loader:
data = data.to(next(self.model.parameters()).device)
logits = self.model(data)
probs = F.softmax(logits, dim=1)
if method == "least_confidence":
scores = self.least_confidence(probs)
elif method == "margin":
scores = self.margin_sampling(probs)
elif method == "entropy":
scores = self.entropy(probs)
all_scores.extend(scores.cpu().numpy())
all_indices.extend(indices.numpy())
selected_indices = np.argsort(all_scores)[-n_samples:]
return [all_indices[i] for i in selected_indices]
import torch
import torch.nn as nn
import torch.nn.functional as F
from sklearn.cluster import KMeans
class BatchActiveLearning:
def __init__(self, model, device="cuda"):
self.model = model
self.device = device
def query_bald(self, unlabeled_loader, n_samples=10, n_dropout=30):
self.model.eval()
all_entropy = []
all_predictions = []
with torch.no_grad():
for indices, data in unlabeled_loader:
data = data.to(self.device)
dropout_probs = []
for _ in range(n_dropout):
self.model.train()
prob = F.softmax(self.model(data), dim=1)
dropout_probs.append(prob)
self.model.eval()
mean_prob = torch.stack(dropout_probs).mean(dim=0)
entropy_mean = -(mean_prob * torch.log(mean_prob + 1e-10)).sum(dim=1)
entropy_dropout = -(dropout_probs * torch.log(dropout_probs + 1e-10)).sum(dim=2).mean(dim=0)
bald_score = entropy_mean - entropy_dropout
all_entropy.extend(bald_score.cpu().numpy())
all_predictions.extend(mean_prob.cpu().numpy())
selected_indices = np.argsort(all_entropy)[-n_samples:]
return selected_indices.tolist()
def query_core_set(self, embeddings, n_samples=10):
n_samples = min(n_samples, len(embeddings))
kmeans = KMeans(n_clusters=n_samples, random_state=42).fit(embeddings)
cluster_centers = kmeans.cluster_centers_
distances = np.linalg.norm(embeddings - cluster_centers[kmeans.labels_], axis=1)
selected_indices = np.argsort(distances)[-n_samples:]
return selected_indices.tolist()
def query_diverse_batch(self, features, probs, n_samples=10, temperature=0.5):
uncertainty = -(probs * torch.log(probs + 1e-10)).sum(dim=1).cpu().numpy()
indices = np.arange(len(features))
selected = []
while len(selected) < n_samples:
remaining = [i for i in indices if i not in selected]
if len(selected) == 0:
best = remaining[np.argmax([uncertainty[i] for i in remaining])]
selected.append(best)
else:
best_score = -np.inf
best_idx = None
for i in remaining:
diversity = min([np.linalg.norm(features[i] - features[s]) for s in selected])
combined = (1 - temperature) * uncertainty[i] + temperature * diversity
if combined > best_score:
best_score = combined
best_idx = i
selected.append(best_idx)
return selected
import torch
import torch.nn as nn
import torch.nn.functional as F
from sklearn.metrics import pairwise_distances
class QueryByCommittee:
def __init__(self, n_models=5):
self.models = []
self.n_models = n_models
def fit(self, train_loader):
for i in range(self.n_models):
model = self._create_model()
self._train_with_bootstrap(model, train_loader, seed=i)
self.models.append(model)
def query(self, unlabeled_loader, n_samples=10):
all_disagreements = []
all_indices = []
with torch.no_grad():
for indices, data in unlabeled_loader:
data = data.to(next(self.models[0].parameters()).device)
predictions = []
for model in self.models:
logits = model(data)
probs = F.softmax(logits, dim=1)
predictions.append(probs)
predictions = torch.stack(predictions)
mean_pred = predictions.mean(dim=0)
variance = ((predictions - mean_pred) ** 2).mean(dim=0)
disagreement = variance.sum(dim=1)
all_disagreements.extend(disagreement.cpu().numpy())
all_indices.extend(indices.numpy())
selected_indices = np.argsort(all_disagreements)[-n_samples:]
return [all_indices[i] for i in selected_indices]
import numpy as np
from scipy.spatial.distance import cdist
class ExpectedModelChange:
def __init__(self, model, unlabeled_loader):
self.model = model
self.unlabeled_loader = unlabeled_loader
def compute_gradients(self, x, y):
self.model.train()
logits = self.model(x)
loss = F.cross_entropy(logits, y)
grads = torch.autograd.grad(loss, self.model.parameters())
return torch.cat([g.view(-1) for g in grads])
def query_egramma(self, labeled_loader, n_samples=10):
self.model.eval()
emc_scores = []
all_indices = []
with torch.no_grad():
for indices, data in unlabeled_loader:
data = data.to(next(self.model.parameters()).device)
logits = self.model(data)
probs = F.softmax(logits, dim=1)
expected_grad_norm = torch.zeros(len(data))
for i in range(len(data)):
p = probs[i]
expected_grad = torch.zeros_like(p)
for c in range(len(p)):
y_onehot = torch.zeros_like(p)
y_onehot[c] = 1.0
grad = self.compute_gradients(data[i:i+1], y_onehot)
expected_grad[c] = grad.norm()
expected_grad_norm[i] = expected_grad.mean()
emc_scores.extend(expected_grad_norm.cpu().numpy())
all_indices.extend(indices.numpy())
selected_indices = np.argsort(emc_scores)[-n_samples:]
return [all_indices[i] for i in selected_indices]
import torch
import torch.nn as nn
import torch.nn.functional as F
from scipy.stats import pearsonr
class ActiveLearningLoop:
def __init__(self, model, unlabeled_dataset, initial_batch_size=100, query_batch_size=20):
self.model = model
self.unlabeled_dataset = unlabeled_dataset
self.initial_batch_size = initial_batch_size
self.query_batch_size = query_batch_size
self.labeled_indices = set()
self.unlabeled_indices = set(range(len(unlabeled_dataset)))
self.sampler = UncertaintySampling(model)
def select_initial_batch(self):
indices = np.random.choice(
list(self.unlabeled_indices),
self.initial_batch_size,
replace=False
)
for idx in indices:
self.labeled_indices.add(idx)
self.unlabeled_indices.discard(idx)
return list(indices)
def query_next_batch(self, unlabeled_loader, method="entropy"):
if len(self.unlabeled_indices) < self.query_batch_size:
return list(self.unlabeled_indices)
selected = self.sampler.query(unlabeled_loader, method, self.query_batch_size)
for idx in selected:
if idx in self.unlabeled_indices:
self.labeled_indices.add(idx)
self.unlabeled_indices.discard(idx)
return selected
def train(self, train_loader, epochs=10):
self.model.train()
optimizer = torch.optim.Adam(self.model.parameters(), lr=1e-3)
for epoch in range(epochs):
for x, y in train_loader:
optimizer.zero_grad()
logits = self.model(x)
loss = F.cross_entropy(logits, y)
loss.backward()
optimizer.step()
return self.model
def evaluate(self, test_loader):
self.model.eval()
correct = 0
total = 0
with torch.no_grad():
for x, y in test_loader:
logits = self.model(x)
predictions = logits.argmax(dim=1)
correct += (predictions == y).sum().item()
total += y.size(0)
return correct / total
Start with a diverse initial labeled set rather than random samples.
Use batch query strategies to avoid selecting similar samples.
Combine uncertainty and diversity for more robust selection.
Monitor learning curves to detect diminishing returns.
Use model ensembles for more stable uncertainty estimates.
Apply temperature scaling before computing uncertainty.
Consider computational cost of querying and training together.
Use warm start models for faster convergence per iteration.
Validate query strategies on small test sets before deployment.
Balance exploration and exploitation in query selection.