Table 2 The properties and applicability of the five clustering approaches.

From: Risk assessment and categorization of terrorist attacks based on the Global Terrorism Database from 1970 to 2020

Clustering methods

Applicable scope

Advantage

Disadvantage

Computational complexity

Representative algorithm

Partitioning method

Medium size set

• Easy and efficient for huge data sets

• With minimal time and space complexity

• The outcome is simple to be locally optimum

• The K value must be predetermined.

• Sensitive to the number of K points chosen

O(n)

FCM, K-means, CLARANS

Hierarchical method

Small quantity set

• Excellent interpretability.

• Generates high-quality clusters

• May be utilized for non-spherical families

• The intricacy of time is tremendous

O(n2 log n)

CURE, BIRCH, CHAMELEON

Density-based method

Any family structure

• Insensitive to noise

• Can detect groups of any form

• The clustering outcomes are tightly tied to the parameters

• Sparser clusters or classes that are closer together perform worse.

O(n log n)

DBSCAN, OPTICS, DENCLUE

Gird-based method

The inherent data density is low

• High velocity

• Parameter dependent

• Unable to handle data with uneven distribution

• The algorithm’s efficiency comes at the expense of the accuracy of the clustering findings

O(n)

STING, CLIQUE, WaveCluster

Model-based method

High-dimensional data

• The outcomes are more visible

• The computational complexity is high

• Ineffective execution

• When the amount of data is little, it does not operate properly

O(n2)

GMM, SOM, COBWEB