Pairs must be keysorted and may also contain variables as keys.
Examples:
?- group_pairs_by_key([1-a,1-b,2-c], Ps).
Ps = [1-[a,b],2-[c]].
?- group_pairs_by_key([X-a,X-b,2-c], Ps).
Ps = [X-[a,b],2-[c]].
Pairs must be keysorted and may also contain variables as keys.
Examples:
?- group_pairs_by_key([1-a,1-b,2-c], Ps).
Ps = [1-[a,b],2-[c]].
?- group_pairs_by_key([X-a,X-b,2-c], Ps).
Ps = [X-[a,b],2-[c]].