Fast, Linear Time, m-Adic Hierarchical Clustering for Search and   Retrieval using the Baire Metric, with linkages to Generalized Ultrametrics,   Hashing, Formal Concept Analysis, and Precision of Data Measurement
  We describe many vantage points on the Baire metric and its use in clustering data, or its use in preprocessing and structuring data in order to support search and retrieval operations. In some cases, we proceed directly to clusters and do not directly determine the distances. We show how a hierarchical clustering can be read directly from one pass through the data. We offer insights also on practical implications of precision of data measurement. As a mechanism for treating multidimensional data, including very high dimensional data, we use random projections. 
Fionn Murtagh and Pedro Contreras
stat.ML