group_by/4

Documentation
- Reference manual
  - The SWI-Prolog library
    - library(solution_sequences): Modify solution sequences
      - distinct/1
      - distinct/2
      - reduced/1
      - reduced/3
      - limit/2
      - offset/2
      - order_by/2
      - group_by/4
- Packages

Availability::- use_module(library(solution_sequences)).(can be autoloaded)

[nondet]group_by(+By, +Template, :Goal, -Bag)

Group bindings of Template that have the same value for By. This predicate is almost the same as bagof/3, but instead of specifying the existential variables we specify the free variables. It is provided for consistency and complete coverage of the common database vocabulary.