Flatten Clustering (RapidMiner Studio Core)

Synopsis

This operator creates a flat clustering model from the given hierarchical clustering model. Clustering is concerned with grouping objects together that are similar to each other and dissimilar to the objects belonging to other clusters.

Description

The Flatten Clustering operator creates a flat cluster model from the given hierarchical cluster model by expanding nodes in the order of their distance until the desired number of clusters (specified by the number of clusters parameter) is reached. In RapidMiner, operators like the Agglomerative Clustering operator provide hierarchical cluster models. The Flatten Clustering operator takes this hierarchical cluster model and an ExampleSet as input and returns a flat cluster model and the clustered ExampleSet. Please note that RapidMiner also provides operators that perform Flat clustering e.g. the K-Means operator.

Flat clustering creates a flat set of clusters without any explicit structure that would relate clusters to each other. Hierarchical clustering creates a hierarchy of clusters. Flat clustering is efficient and conceptually simple, but it has a number of drawbacks. These algorithms return a flat unstructured set of clusters, require a prespecified number of clusters as input and are nondeterministic. Hierarchical clustering outputs a hierarchy, a structure that is more informative than the unstructured set of clusters returned by flat clustering. Hierarchical clustering does not require us to prespecify the number of clusters and most hierarchical algorithms that have been used in information retrieval are deterministic. These advantages of hierarchical clustering come at the cost of lower efficiency.

Clustering is concerned with grouping together objects that are similar to each other and dissimilar to the objects belonging to other clusters. It is a technique for extracting information from unlabeled data and can be very useful in many different scenarios e.g. in a marketing application we may be interested in finding clusters of customers with similar buying behavior.

Input

hierarchical (Hierachical Cluster Model)
This port expects the hierarchical cluster model. Hierarchical clustering operators like the Agglomerative Clustering operator generate such a model.
example set (Data Table)
The input port expects an ExampleSet. It is the output of the Agglomerative Clustering operator in the attached Example Process. The output of other operators can also be used as input.

Output

flat (Cluster Model)
This port delivers the flat cluster model which has information regarding the clustering performed. It tells which examples are part of which cluster.
example set (Data Table)
The ExampleSet that was given as input is passed with minor changes to the output through this port. An attribute with id role is added to the input ExampleSet to distinguish examples.

Parameters

number_of_clustersThis parameter specifies the desired number of clusters to form. There is no hard and fast rule to form a number of clusters. But, generally it is preferred to have a small number of clusters with examples scattered (not too scattered) around them in a balanced way. Range: integer
add_as_labelIf true, the cluster id is stored in an attribute with the label role instead of cluster role. Range: boolean
remove_unlabeledIf set to true, unlabeled examples are deleted. Range: boolean

Tutorial Processes

Flattening the Agglomerative Cluster model

The 'Iris' data set is loaded using the Retrieve operator. A breakpoint is inserted at this step so that you can have a look at the ExampleSet. The Agglomerative Clustering operator is applied on this ExampleSet. Run the process and switch to the Results Workspace. Note the Graph View of the results. You can see that the algorithm has not created separate groups or clusters as other clustering algorithms (like k-means), instead the result is a hierarchy of clusters. Under the Folder View you can see members of each cluster in folder format. You can see that it is an hierarchy of folders. The Dendogram View shows the dendrogram for this clustering which shows how single-element clusters were joined step by step to make a hierarchy of clusters. The ExampleSet and the hierarchical cluster model returned by this operator are provided as input to the Flatten Clustering operator.

The Flatten Clustering operator is applied with default values for all parameters. Run the process and you will see that two new attributes are created by the Flatten Clustering operator. The id attribute is created to distinguish examples clearly. The cluster attribute is created to show which cluster the examples belong to. As the parameter number of clusters was set to 3, only three clusters are possible. That is why each example is assigned to 'cluster_0', 'cluster_1' or 'cluster_2'. Also note the Plot View of this data. You can clearly see how the algorithm has created three separate groups in the Plot View. A cluster model is also delivered through the cluster model output port. It has information regarding the clustering performed. Under Folder View you can see members of each cluster in folder format.