
group_by_key(+Key, +Structs, -Grouped)

   Partition a list into sublists by key

Arguments
   Key                 Key argument position (non-negative integer, or list of those)
   Structs             List of structures
   Grouped             Variable, or list of list of structures

Type
   library(lists_of_structures)

Description

    The list Structs is partitioned into maximal sublists of consecutive
    elements with identical keys.  Concatenating all these sublists will
    yield the original list.  If the original list was ordered according
    to the Key'th argument, then the sublists represent a partitioning of
    the original elements according to their different key values.
    

Modes and Determinism
   group_by_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_by_key(1, [f(a,1),f(a,2),f(b,2),f(c,2),f(c,5)], Groups).
    Groups = [[f(a,1),f(a,2)], [f(b,2)], [f(c,2),f(c,5)]]
    Yes (0.00s cpu)

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

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



See Also
   group_with_key / 3, same_key_prefix / 5, sort / 4, merge / 5
