WordNet (r) 3.0 (2006):

pigeonholing
    n 1: a system for classifying things into groups [syn:
         grouping, pigeonholing]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "pigeonholing":
   analysis, arrangement, cataloging, categorization, classification,
   codification, division, filing, grading, grouping, indexing,
   placement, ranging, ranking, rating, sorting, stratification,
   subdivision, tabulation, taxonomy, typology