At the European Summer University in Digital Humanities 2016 I was luck to be able to attend some sessions on Stylometry run by Maciej Eder. In his historical review he mentioned people like Valla and Mendenhall, but also mentioned a fellow Pole, Wincenty Lutoslawksi whose book The origin and growth of Plato’s logic; with an account of Plato’s style and of the chronology of his writings (1897) is the first to use the term “stylometry”. Lutoslawski develops a Theory of Stylometry and reviewed “500 peculiarities of Plato’s style” as part of his work on Plato’s logic. The nice thing is that the book is available through the Internet Archive.
Eder has a nice page about the work he and ogthers in the Computational Stylistics Group are doing. In the workshop sessions I was able to attend he showed us how to set up and run his “stylo” package (PDF) that provides a simple user interface over R for doing stylometry. He also showed us how to then use Gephi for network visualization.