Document categorisation system

A document categorization system, including a clusterer for generating clusters of related electronic documents based on features extracted from the documents, and a filter module for generating a filter on the basis of the clusters to categorize further documents received by the system. The system may include an editor for manually browsing and modifying the clusters. The categorization of the documents is based on n-grams, which are used to determine significant features of the documents. The system includes a trend analyzer for determining trends of changing document categories over time, and for identifying novel clusters. The system may be implemented as a plug-in module for a spreadsheet application for permitting one-off or ongoing analysis of text entries in a worksheet.