K-Nearest Neighbors

function knn(data, query, k) {
  // 1. Calculate distances
  const distances = data.map(point => ({
    label: point.label,
    dist: Math.sqrt(
      (point.x - query.x) ** 2 +
      (point.y - query.y) ** 2
    )
  }));
  
  // 2. Sort by distance
  distances.sort((a, b) => a.dist - b.dist);
  
  // 3. Get K nearest
  const kNearest = distances.slice(0, k);
  
  // 4. Vote!
  const votes = {};
  kNearest.forEach(n => {
    votes[n.label] = (votes[n.label] || 0) + 1;
  });
  
  // Return majority vote
  return Object.entries(votes)
    .sort((a, b) => b[1] - a[1])[0][0];
}