
group_values_with_key(+KeyPos, +ValPos, +Structs, -Grouped)

   Partition a list into sublists by key

Arguments
   KeyPos              Key argument position (positive integer, or list of those)
   ValPos              Value argument position (positive integer, or list of those)
   Structs             List of structures
   Grouped             Variable, or list of Key-ValueList structures

Type
   library(lists_of_structures)

Description

    The list Structs is partitioned into maximal sublists of consecutive
    elements with identical keys.  If the original list was ordered according
    to the KeyPos'th argument, then the sublists represent a partitioning of
    the original elements according to their different key values.
    From each of these sublists, the ValPos'th arguments are extraced
    to form a ValueList for the corresponding key.
    
    The output argument Grouped is bound to a list of Key-ValueList pairs,
    where Key is the value of the KeyPos'th argument that all the values
    in ValueList have in common.
    

Modes and Determinism
   group_values_with_key(+, +, +, -) is det

Exceptions
     4 --- Arguments are insufficiently instantiated
     5 --- Some argument or its components are of the wrong type
     6 --- Some structure does not have a Key'th argument

Examples
   
    ?- group_values_with_key(1, 2, [f(a,1), f(a,2), f(b,2), f(c,2), f(c,5)], Groups).
    Groups = [a - [1,2], b - [2], c - [2,5]]
    Yes (0.00s cpu)

    ?- group_values_with_key(2, 1, [f(a,1), f(a,2), f(b,2), f(c,2), f(c,5)], Groups).
    Groups = [1 - [a], 2 - [a,b,c], 5 - [c]]
    Yes (0.00s cpu)


See Also
   group_with_key / 3
