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ADDED: group_pairs_by_key/2

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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]].
This commit is contained in:
Markus Triska
2020-04-14 00:10:33 +02:00
parent 15d18484e3
commit 237c855f10
1 changed files with 12 additions and 0 deletions
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12
src/prolog/lib/pairs.pl
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@@ -1,6 +1,7 @@
:- module(pairs, [pairs_keys_values/3,
pairs_keys/2,
pairs_values/2,
group_pairs_by_key/2,
map_list_to_pairs/3]).
@@ -19,3 +20,14 @@ map_list_to_pairs2([], _, []).
map_list_to_pairs2([H|T0], Pred, [K-H|T]) :-
call(Pred, H, K),
map_list_to_pairs2(T0, Pred, T).
group_pairs_by_key([], []).
group_pairs_by_key([K-V|KVs0], [K-[V|Vs]|KVs]) :-
same_key(K, KVs0, Vs, KVs1),
group_pairs_by_key(KVs1, KVs).
same_key(K0, [K1-V|KVs0], [V|Vs], KVs) :-
K0 == K1, !,
same_key(K0, KVs0, Vs, KVs).
same_key(_, KVs, [], KVs).