Types of Clusterings a clustering is a set of clusters Important distinction between hierarchical and partitional sets of clusters Partitional Clustering a division data objects into non-overlapping subsets (clusters)such that each data object is in exactly one subset Hierarchical clustering A set of nested clusters organized as a hierarchical tree 16
16 Types of Clusterings ◼ A clustering is a set of clusters ◼ Important distinction between hierarchical and partitional sets of clusters ◼ Partitional Clustering ◼ A division data objects into non-overlapping subsets (clusters) such that each data object is in exactly one subset ◼ Hierarchical clustering ◼ A set of nested clusters organized as a hierarchical tree
Quality: What s g。。 d clustering A good clustering method will produce high quality clusters with high intra-class similarity low inter-class similarity The guality of a clustering result depends on both the similarity measure used by the method and its implementation The guality of a clustering method is also measured by its ability to discover some or all of the hidden patterns 17
17 Quality: What Is Good Clustering? ◼ A good clustering method will produce high quality clusters with ◼ high intra-class similarity ◼ low inter-class similarity ◼ The quality of a clustering result depends on both the similarity measure used by the method and its implementation ◼ The quality of a clustering method is also measured by its ability to discover some or all of the hidden patterns
Types of clusters: Well-Separated Well-Separated clusters a cluster is a set of points such that any point in a cluster is closer (or more similar) to every other point in the cluster than to any point not in the cluster 3 well-separated clusters
18 Types of Clusters: Well-Separated ◼ Well-Separated Clusters: ◼ A cluster is a set of points such that any point in a cluster is closer (or more similar) to every other point in the cluster than to any point not in the cluster. 3 well-separated clusters
Types of clusters: Center-Based Center-based a cluster is a set of objects such that an object in a cluster is closer(more similar) to the center of a cluster, than to the center of any other cluster The center of a cluster is often a centroid the average of all the points in the cluster, or a medoid the most representative" point of a cluster 4 center-based clusters
19 Types of Clusters: Center-Based ◼ Center-based ◼ A cluster is a set of objects such that an object in a cluster is closer (more similar) to the “center” of a cluster, than to the center of any other cluster ◼ The center of a cluster is often a centroid, the average of all the points in the cluster, or a medoid, the most “representative” point of a cluster 4 center-based clusters
Types of clusters: Contiguity-Based Contiguous Cluster(Nearest neighbor or Transitive) A cluster is a set of points such that a point in a cluster is closer (or more similar) to one or more other points in the cluster than to any point not in the cluster 8 contiguous clusters
20 Types of Clusters: Contiguity-Based ◼ Contiguous Cluster (Nearest neighbor or Transitive) ◼ A cluster is a set of points such that a point in a cluster is closer (or more similar) to one or more other points in the cluster than to any point not in the cluster. 8 contiguous clusters