How to calculate the silhouette score for different cluster?

Jennnnnny

Hello,

I'm actually trying to calculate the silhouette score for each of my clusters, any ideas?

Ioannis

I don't know if my logic is correct or there is faster way to do it since I'm pretty new to DSS and my solution is more coding-oriented. One way I can think of is to create a csv with the results [x1, x2, ..., xn, clusters] and then you can create a python recipe or notebook to calculate the silhouette score. Points should be a double with your features, clusters a list with the clusters values (0,1,2...) and you should also calculate the centroids for each cluster.

from typing import List
import numpy as np

def centroids(points: np.array, clusters: np.array)->List:
    centroids = []
    for i in range(3):
       indices = np.where(clusters == i)
       cluster_points = points[indices]
       centroids.append(cluster_points.mean(axis=0))
    return centroids

def euclidean_dist(x1: np.array, x2: np.array) -> float:
    
    dist = np.sqrt(sum((x1 - x2)**2))
    return dist


def silhouette_score(points:List, clusters:List, centroids:List) -> List:
  

    if type(points) is list:
        points = np.asarray(points)
        clusters = np.asarray(clusters)
        centroids = np.asarray(centroids)

        
    silhouette_scores = []
    no_clusters = clusters.max() + 1

    for i in range(no_clusters):

        # Calculate a(i)
        indices = np.where(clusters == i)
        cluster_points = points[indices]
        dist = 0
        for c in cluster_points:
            dist += euclidean_dist(centroids[i], c)
        a_i = dist/len(cluster_points)

        # Calculate b(i)
        dist = []
        for c in centroids:
            dist.append(euclidean_dist(centroids[i], c))
        dist = np.asarray(dist)

        closest_centroid = np.argsort(dist)[1]
        indices = np.where(clusters == closest_centroid)
        cluster_points = points[indices]
        dist = 0
        for c in cluster_points:
            dist += euclidean_dist(centroids[i], c)
        b_i = dist/len(cluster_points)

        # Silhouette score of a single cluster
        s_i = (b_i - a_i) / max(b_i, a_i)

        silhouette_scores.append(s_i)

    return silhouette_scores

.