Hierarchical clustering of massive, high dimensional data sets by exploiting ultrametric embedding

Coding of data, usually upstream of data analysis, has crucial implications for the data analysis results. By modifying the data coding-through use of less than full precision in data values-we can aid appreciably the effectiveness and efficiency of the hierarchical clustering. In our first application, this is used to lessen the quantity of data to be hierarchically clustered. The approach is a hybrid one, based on hashing and on the Ward minimum variance agglomerative criterion. In our second application, we derive a hierarchical clustering from relationships between sets of observations, rather than the traditional use of relationships between the observations themselves. This second application uses embedding in a Baire space, or longest common prefix ultrametric space. We compare this second approach, which is of O(n log n) complexity, to k-means.