Group values with equivalent (==/2)
consecutive keys. For example:
?- group_pairs_by_key([a-2, a-1, b-4, a-3], X).
X = [a-[2,1], b-, a-]
Sorting the list of pairs before grouping can be used to group
all values associated with a key. For example, finding all values
associated with the largest key:
?- sort(1, @>=, [a-1, b-2, c-3, a-4, a-5, c-6], Ps),
K = c,
Vs = [3, 6].
In this example, sorting by key only (first argument of sort/4
is 1) ensures that the order of the values in the original list of pairs
|Pairs ||Key-Value list |
|Joined ||List of Key-Group, where
Group is the list of Values associated with equivalent
consecutive Keys in the same order as they appear in Pairs. |