Clustering device and clustering method

A clustering device, comprising:

• a clustering section configured to classify multiple element data into clusters;
• and
• an evaluation score calculation section configured to:
• using calculated values obtained during a calculation process by the clustering section for classification of the multiple element data,
• calculate a degree of internal compactness that is a first sum of values, each being defined by normalizing a first index value by a first value that is based on a number of element data within each cluster, the first index value indicating a degree of dispersion of element data within each cluster;
• calculate a degree of external separation defined by normalizing a second sum of second index values for each cluster by a second value that is based on a number of clusters, each of the second index values indicating an index of a distance between the clusters;
• and
• calculate an evaluation score for evaluating a classification result by the clustering section according to a predetermined formula defined by the degree of internal compactness and the degree of external separation which are variables.

A clustering method, comprising:

• a batch process step of obtaining an optimum number of clusters from evaluation scores obtained by classifying all element data into clusters while changing a number of clusters to evaluate classification results for each of the number of clusters, and obtaining a classification result of classifying all element data into clusters with the optimum number of clusters;
• an update process step of assigning, upon addition of new element data after the batch process step, the new element data to one of existing clusters, and calculating an evaluation score for evaluating a classification result after assigning the new element data to the one of the existing clusters;
• and
• a determining step of determining validity of the classification result in the update process step, based on the evaluation score calculated in the update process step.