noun (n)

• a group of people or things arranged by class or category(noun.group)

  Synonym:
  categorization, classification
  

  source: wordnet30
• the basic cognitive process of arranging into classes or categories(noun.cognition)

  Synonym:
  categorization, classification, sorting
  

  source: wordnet30
• the act of distributing things into classes or categories of the same type(noun.act)

  Synonym:
  assortment, categorization, classification, compartmentalisation, compartmentalization
  

  source: wordnet30