Arranging in sorts or ranks.
- Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874. (verb) (v. impers.) (verb, impersonal)

Usage examples:

You know, he explained to Lapham, that we have to look at all these facts as material, and we get the habit of classifying them.
- Entire PG Edition of The Works of William Dean Howells by William Dean Howells
Just as the daylight was departing, and he was sitting at his large table near the window, again checking and classifying the documents and plans connected with his invention, he was surprised to see his old master and friend Bertheroy enter the workroom.
- Paris From the "Three Cities" by Emile Zola
He was absent for three years and spent thirteen more in studying and classifying the material he had collected.
- American Men of Mind by Burton E. Stevenson