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name: ds-community-detection compatibility: opencode completeness: 95 content-types:

• code
• guidance
• do-dont
• examples description: '"Detects communities and clusters in graphs using modularity optimization spectral methods, and graph partitioning algorithms"' license: MIT maturity: stable metadata: domain: coding output-format: code related-skills: ds-association-rules, ds-clustering, ds-dimensionality-reduction role: implementation scope: implementation triggers: community detection, graph clustering, modularity, spectral clustering graph partitioning archetypes:
  • tactical
  • generation anti_triggers:
  • brainstorming
  • vague ideation
  • code golf
  • over-engineering response_profile: verbosity: low directive_strength: high abstraction_level: operational version: "1.0.0"

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Community Detection

Comprehensive guide to community detection in machine learning and data science workflows.

When to Use This Skill

• Solving real-world unsupervised learning problems
• Building machine learning pipelines with community detection
• Implementing best practices for community detection
• Optimizing model performance using community detection techniques
• Learning industry-standard approaches to community detection

When NOT to Use This Skill

• When using pre-built libraries without understanding underlying concepts
• For toy problems that don't require community detection rigor
• When domain expertise in specific problem requires different approach
• If your problem doesn't require the complexity this skill provides

Purpose and Key Concepts

Community Detection is a critical component of the machine learning workflow. This skill covers:

1. Theoretical foundations — Mathematical principles and statistical concepts
2. Practical implementation — Working code examples and patterns
3. Common pitfalls — Mistakes to avoid and how to recover from them
4. Best practices — Industry-standard approaches and optimization techniques

Core Workflow

1. Understand the problem — Clearly define what you're solving for
2. Select approach — Choose the right technique for your data and constraints
3. Implement solution — Write clean, tested code following best practices
4. Validate results — Verify your implementation with tests and validation
5. Optimize performance — Improve efficiency and accuracy incrementally

Implementation Patterns

Pattern 1: Basic Community Detection

import networkx as nx
import numpy as np
from typing import Dict, Any

def basic_community_detection(graph: nx.Graph) -> Dict[str, Any]:
    """Basic community detection using greedy modularity optimization."""
    communities = nx.community.greedy_modularity_communities(graph)
    community_labels = {node: idx for idx, comm in enumerate(communities) for node in comm}
    modularity = nx.community.modularity(graph, communities)
    return {
        'communities': communities
        'labels': community_labels
        'modularity': float(modularity)
    }

# Create a sample graph with known community structure
G = nx.gnm_random_graph(50, 150, seed=42)
for i in range(0, 25):
    for j in range(i+1, 25):
        if np.random.rand() < 0.3:
            G.add_edge(i, j)
    for i in range(25, 50):
        for j in range(i+1, 50):
            if np.random.rand() < 0.3:
                G.add_edge(i, j)

results = basic_community_detection(G)
print(f"Detected {len(results['communities'])} communities with modularity Q={results['modularity']:.4f}")

Pattern 2: Production-Ready Community Detection

import logging
import networkx as nx
import numpy as np
from typing import Any, Dict, Union
from sklearn.cluster import SpectralClustering

logger = logging.getLogger(__name__)

class CommunityDetection:
    """Production implementation of Community Detection using spectral methods"""
    
    def __init__(self, n_communities: int = 4, method: str = "spectral"):
        self.n_communities = n_communities
        self.method = method
        
    def execute(self, graph: Union[nx.Graph, np.ndarray]) -> Dict[str, Any]:
        """Execute Community Detection on graph data"""
        try:
            if isinstance(graph, np.ndarray):
                G = nx.from_numpy_array(graph)
            elif isinstance(graph, nx.Graph):
                G = graph.copy()
            else:
                raise TypeError("Input must be a NetworkX graph or adjacency matrix")
                
            if self.method == "spectral":
                adj_matrix = nx.to_numpy_array(G)
                sc = SpectralClustering(n_clusters=self.n_communities, affinity='precomputed')
                labels = sc.fit_predict(adj_matrix)
                communities = {int(i): list(np.where(labels == i)[0]) for i in range(self.n_communities)}
                modularity = nx.community.modularity(G, communities.values())
            else:
                communities = list(nx.community.greedy_modularity_communities(G))
                labels = np.array([community_labels[node] for node in G.nodes()])
                modularity = nx.community.modularity(G, communities)
                
            return {
                'status': 'success'
                'communities': communities
                'labels': labels.tolist()
                'modularity': float(modularity)
                'node_count': G.number_of_nodes()
                'edge_count': G.number_of_edges()
            }
        except Exception as e:
            logger.error(f"Community detection failed: {e}")
            return {'status': 'error', 'message': str(e)}

Pattern 3: BAD vs GOOD Implementation

# BAD: Hardcoded values, no error handling, violates DRY principle
def bad_detection(G):
    labels = [0] * G.number_of_nodes()
    for i in range(10):
        labels[i] = 1
    return labels

# GOOD: Type hints, validation, modular design, follows SOLID principles
def good_detection(graph: nx.Graph, n_clusters: int = 4) -> list[int]:
    if not isinstance(graph, nx.Graph):
        raise TypeError("Expected NetworkX graph")
    if graph.number_of_nodes() == 0:
        raise ValueError("Graph is empty")
    adj = nx.to_numpy_array(graph)
    sc = SpectralClustering(n_clusters=n_clusters, affinity='precomputed')
    return sc.fit_predict(adj).tolist()

Best Practices

• ✅ Always validate your implementation on test data
• ✅ Document your assumptions and methodology
• ✅ Use version control for reproducibility
• ✅ Monitor performance metrics in production
• ✅ Periodically review and update your approach
• ✅ Test with edge cases and outliers
• ✅ Log all significant operations for debugging

Common Pitfalls

| Pitfall | Problem | Solution | |

---

---

Constraints

MUST DO

• Validate all data preprocessing steps are fit-only on training data, never on validation or test sets
• Implement reproducible pipelines with fixed random seeds and deterministic operations where possible
• Report model performance with confidence intervals via bootstrapping or cross-validation across multiple runs
• Log all experiments with parameters, metrics, and artifacts using MLflow or equivalent tracking system

MUST NOT DO

• Do not evaluate a model on the same data used for training — always hold out a proper test set
• Avoid overfitting to the validation set by limiting hyperparameter search iterations
• Never use features that can only be computed at inference time (look-ahead bias)
• Do not report single-run accuracy without statistical significance testing or error bars

Live References

Authoritative documentation links for this skill's domain. The model follows markdown links at load time to resolve external references and inline content.

• Community Detection — Wikipedia
• NetworkX Community Detection Module
• Louvain Method Implementation (python-louvain)
• Graph Community Structure — Complex Networks Lecture Notes
• Leiden Algorithm — Traag et al.