python - unexpected sklearn dbscan result

Question

i have implemented a simple code to cluster simple array of point's but the result's are unexpected.

code:

from pandas import DataFrame
import matplotlib.pyplot as plt
import matplotlib
from sklearn.cluster import DBSCAN

x1 = [[10.0, 1.0], [10.0, 2.0], [10.0, 10.0], [10.0, 10.0], [10.0, 23.0], [10.0, 22.0]]
x2 = [[20.0, 2.0], [20.0, 15.0], [20.0, 26.0], [20.0, 13.0], [20.0, 32.0], [20.0, 35.0]]
x3 = [[30.0, 25.0], [30.0, 28.0], [30.0, 17.0], [30.0, 16.0], [30.0, 15.0], [30.0, 38.0]]
x4 = [[40.0, 1.0], [40.0, 2.0], [40.0, 16.0], [40.0, 41.0], [40.0, 40.0], [40.0, 39.0]]
x5 = [[60.0, 1.0], [60.0, 10.0], [60.0, 12.0], [60.0, 32.0], [60.0, 33.0], [60.0, 50.0]]

df1 = DataFrame(data= x1) 
df2 = DataFrame(data= x2)
df3 = DataFrame(data= x3)
df4 = DataFrame(data= x4)
df5 = DataFrame(data= x5)

data = df5

dbscan_opt=DBSCAN(eps=1,min_samples=2)
dbscan_opt.fit(data[[0,1]])
data['DBSCAN_opt_labels']=dbscan_opt.labels_
data['DBSCAN_opt_labels'].value_counts()

# Plotting the resulting clusters
colors=['purple','red','blue','green']
plt.figure(figsize=(6,6))
plt.scatter(data[0],data[1],c=data['DBSCAN_opt_labels'],cmap=matplotlib.colors.ListedColormap(colors),s=60)
plt.title('DBSCAN Clustering',fontsize=20)
plt.xlabel('Feature 1',fontsize=14)
plt.ylabel('Feature 2',fontsize=14)
plt.show()

results:

Red circle means that i expect a cluster but the algorithm detect them as noise points..

could you help me to fix parameter's of DBSCAN to detect them as well?

thank you!

Answer 1

i found the problem. limited color list. i should add more colors because DBSCAN generates new cluster but with same color and that was my mistake.

so this is working fine now:

dbscan_opt=DBSCAN(eps=3.0,min_samples=1).fit(data[[0,1]])

data['DBSCAN_opt_labels']=dbscan_opt.labels_
data['DBSCAN_opt_labels'].value_counts()

print(data)

# Plotting the resulting clusters
colors=['purple','red','blue','green', 'magenta', 'teal', 'black']
plt.figure(figsize=(6,6))
plt.scatter(data[0],data[1],c=data['DBSCAN_opt_labels'],cmap=matplotlib.colors.ListedColormap(colors),s=60)
plt.title('DBSCAN Clustering',fontsize=20)
plt.xlabel('Feature 1',fontsize=14)
plt.ylabel('Feature 2',fontsize=14)
plt.show()