PrologJ Support for Set Operations

Builtin Predicates

The PrologJ set processing extension adds a number of built-in predicates for manipulating sets. (The predicates that accept sets as input(s) also accept bag as input(s).)

• filter_set(SetOrBag, Template, Predicate, Result)
   
  
  • SetOrBag is a set or bag represented as a (possibly empty) list
     
  • Template is a term that is unified with each successive element of SetOrBag in turn.
     
    
  • Predicate is called (as by once/1) once for each successive element of SetOrBag in turn, provided unification with Template is successful. (Typically, Template and Predicate have one or more variables in common.)
     
  • Result is unified with a list consisting of each element of SetOrBag that successfully unified with Template and then satisfied Predicate. (If there is no such element, Result is unified with the empty list.) The elements in this list occur in the same order in which they appeared in BagOrSet, and duplicate elements are preserved. The predicate filter_set/4 succeeds just when this unification is successful. It is not redoable.  
    Note: filter_set/4 should only be used with crisp sets. Either fuzzy_filter_set/4 or fuzzy_filter_set/5 should be used with fuzzy sets.
     
    Example:

      	filter_set([ color(apple, red), color(banana, yellow), color(tomato, red) ],
      				 color(Fruit, Color), Color = red, Result).
      	

    unifies Result with

      	[ color(apple, red), color(tomato, red) ]
      	

  • Error Cases:
     

    Conditions	Error Term
    SetOrBag is a variable	instantiation_error
    SetOrBag is neither a variable nor a proper list nor the empty list	type_error(list, SetOrBag)
    SetOrBag is a list that contains an element that is a variable	instantiation_error
    SetOrBag is a list that contains an element such that, after it is unified with Template, Predicate is a variable	instantiation_error
    SetOrBag is a list that contains an element such that, after it is unified with Template, Predicate is neither a variable nor an atom nor a compound term	type_error(callable, Predicate)
    Result is neither a variable, nor a proper or partial list, nor the empty list	type_error(list, Result)

   
  
• findset(Term, Goal, Set)
   
  This predicate is similar to findall/3, except that the result is guaranteed to be a set; if it is a bag, duplicates are eliminated to make it a set. The result set is in the order determined by the term_precedes relationship, as with the ISO Prolog predicate setof/3. The error cases are the same as specified in the ISO standard for findall/3.
   
• set_difference(SetOrBag1, SetOrBag2, Set12)
   
  
  • SetOrBag1 and SetOrBag1 are sets or bags represented as (possibly empty) lists. However, if either is a bag, it is converted to a set by eliminating duplicate elements.
     
  • Set12 is unified with a list that corresponds to the difference of the sets represented by the first and second arguments. An element appears in the result if it appears in SetOrBag1, but not in SetOrBag2. An element appears in the result just once, regardless of how many times it may appear in the first input argument. The result is always in the order determined by the term_precedes relationship, as with the ISO Prolog predicate setof/3.
     
    This built-in predicate may also be used to form the complement of a set relative to some universe, by taking the difference of the universal set minus the set to be complemented. If this is going to be done frequently in a program, it is helpful to ensure that the universe is represented by a list that includes each element just once, in the order determined by the term-precedes relationship.
     
    Example:

        set_difference([ bananas, figs, apples ], [ apples, cumquats, figs ], Set12).
        

    Unifies Set12 with

        [ bananas ]
        

  • Error Cases:
     

    Conditions	Error Term
    SetOrBag1 is a variable	instantiation_error
    SetOrBag1 is neither a variable nor a proper list nor the empty list	type_error(list, SetOrBag1)
    SetOrBag1 is a list that contains an element that is a variable	instantiation_error
    SetOrBag2 is a variable	instantiation_error
    SetOrBag2 is neither a variable nor a proper list nor the empty list	type_error(list, SetOrBag2)
    SetOrBag2 is a list that contains an element that is a variable	instantiation_error
    Set12 is neither a variable, nor a proper or partial list, nor the empty list	type_error(list, Result)

   
  
• set_intersection(SetOrBag1, SetOrBag2, Set12)
   
  
  • SetOrBag1 and SetOrBag1 are sets or bags represented as (possibly empty) lists. However, if either is a bag, it is converted to a set by eliminating duplicate elements.
     
  • Set12 is unified with a list that corresponds to the intersection of the sets represented by the first and second arguments. An element appears in the result if it appears in both of SetOrBag1 and SetOrBag2. An element appears in the result just once, regardless of how many times it may appear in the input arguments. The result is always in the order determined by the term_precedes relationship, as with the ISO Prolog predicate setof/3.  
    Example:

        set_intersection([ bananas, figs, apples ], [ apples, cumquats, figs ], Set12).
        

    Unifies Set12 with

        [ apples, figs ]
        

  • Error Cases:
     

    Conditions	Error Term
    SetOrBag1 is a variable	instantiation_error
    SetOrBag1 is neither a variable nor a proper list nor the empty list	type_error(list, SetOrBag1)
    SetOrBag1 is a list that contains an element that is a variable	instantiation_error
    SetOrBag2 is a variable	instantiation_error
    SetOrBag2 is neither a variable nor a proper list nor the empty list	type_error(list, SetOrBag2)
    SetOrBag2 is a list that contains an element that is a variable	instantiation_error
    Set12 is neither a variable, nor a proper or partial list, nor the empty list	type_error(list, Result)

   
  
• set_union(SetOrBag1, SetOrBag2, Set12)
   
  
  • SetOrBag1 and SetOrBag1 are sets or bags represented as (possibly empty) lists. However, if either is a bag, it is converted to a set by eliminating duplicate elements.
     
  • Set12 is unified with a list that corresponds to the union of the sets represented by the first and second arguments. An element appears in the result if it appears in either of SetOrBag1 or SetOrBag2. An element appears in the result just once, regardless of how many times it may appear in either of the input arguments, or if it appears in both. The result is always in the order determined by the term_precedes relationship, as with the ISO Prolog predicate setof/3.
     
    This built-in predicate may also be used to convert a bag to a set, by taking the union of the bag with the empty set ([]).
       
    Example:

        set_union([ bananas, figs, apples ], [ apples, cumquats, figs ], Set12).
        

    Unifies Set12 with

        [ apples, bananas, cumquats, figs ]
        

  • Error Cases:
     

    Conditions	Error Term
    SetOrBag1 is a variable	instantiation_error
    SetOrBag1 is neither a variable nor a proper list nor the empty list	type_error(list, SetOrBag1)
    SetOrBag1 is a list that contains an element that is a variable	instantiation_error
    SetOrBag2 is a variable	instantiation_error
    SetOrBag2 is neither a variable nor a proper list nor the empty list	type_error(list, SetOrBag2)
    SetOrBag2 is a list that contains an element that is a variable	instantiation_error
    Set12 is neither a variable, nor a proper or partial list, nor the empty list	type_error(list, Result)

   
  

Copyright © 2005 - Russell C. Bjork. See the file See file COPYING in the root directory for copyright information.