The Porter Stemming Algorithm
This is the ‘official’ home page for distribution of the Porter Stemming Algorithm, written and maintained by its author, Martin Porter.
The Porter stemming algorithm (or ‘Porter stemmer’) is a process for removing the commoner morphological and inflexional endings from words in English. Its main use is as part of a term normalisation process that is usually done when setting up Information Retrieval systems.
The algorithm was originally described in Porter, M.F., 1980, An algorithm for suffix stripping, Program, 14(3) :130-137. It has since been reprinted in Sparck Jones, Karen, and Peter Willet, 1997, Readings in Information Retrieval, San Francisco: Morgan Kaufmann, ISBN 1-55860-454-4.
The Algorithm has been widely used, quoted, and adapted over the past 20 years. Unfortunately variants of it abound which claim to be true implementations, and this can cause confusion. This page contains a demonstration of the stemmer, and downloadable versions of it in ANSI C, Java, Perl and other languages.
The original stemmer was coded up in BCPL, a language no longer in vogue. In its final surviving form, this BCPL version has three minor points of difference from the published algorithm, and these are clearly marked in the downloadable ANSI C version. They are discussed further below.
The ANSI C, Java and Perl versions are exactly equivalent to the original BCPL version, having been tested on a large corpus of English text. The original paper was, I hope, unambiguous, despite a couple of irritating typos, but even so the ANSI C version nowadays acts as a better definition of the algorithm than the original published paper.