1/* Part of SWI-Prolog 2 3 Author: Jan Wielemaker 4 E-mail: J.Wielemaker@vu.nl 5 WWW: http://www.swi-prolog.org 6 Copyright (c) 2006-2015, University of Amsterdam 7 VU University Amsterdam 8 All rights reserved. 9 10 Redistribution and use in source and binary forms, with or without 11 modification, are permitted provided that the following conditions 12 are met: 13 14 1. Redistributions of source code must retain the above copyright 15 notice, this list of conditions and the following disclaimer. 16 17 2. Redistributions in binary form must reproduce the above copyright 18 notice, this list of conditions and the following disclaimer in 19 the documentation and/or other materials provided with the 20 distribution. 21 22 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 23 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 24 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 25 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 26 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 27 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 28 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 29 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 30 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 32 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 33 POSSIBILITY OF SUCH DAMAGE. 34*/ 35 36:- module(pairs, 37 [ pairs_keys_values/3, 38 pairs_values/2, 39 pairs_keys/2, 40 group_pairs_by_key/2, 41 transpose_pairs/2, 42 map_list_to_pairs/3 43 ]). 44 45/** <module> Operations on key-value lists 46 47This module implements common operations on Key-Value lists, also known 48as _Pairs_. Pairs have great practical value, especially due to 49keysort/2 and the library assoc.pl. 50 51This library is based on disussion in the SWI-Prolog mailinglist, 52including specifications from Quintus and a library proposal by Richard 53O'Keefe. 54 55@see keysort/2, library(assoc) 56@author Jan Wielemaker 57*/ 58 59%! pairs_keys_values(?Pairs, ?Keys, ?Values) is det. 60% 61% True if Keys holds the keys of Pairs and Values the values. 62% 63% Deterministic if any argument is instantiated to a finite list 64% and the others are either free or finite lists. All three lists 65% are in the same order. 66% 67% @see pairs_values/2 and pairs_keys/2. 68 69pairs_keys_values(Pairs, Keys, Values) :- 70 ( nonvar(Pairs) -> 71 pairs_keys_values_(Pairs, Keys, Values) 72 ; nonvar(Keys) -> 73 keys_values_pairs(Keys, Values, Pairs) 74 ; values_keys_pairs(Values, Keys, Pairs) 75 ). 76 77pairs_keys_values_([], [], []). 78pairs_keys_values_([K-V|Pairs], [K|Keys], [V|Values]) :- 79 pairs_keys_values_(Pairs, Keys, Values). 80 81keys_values_pairs([], [], []). 82keys_values_pairs([K|Ks], [V|Vs], [K-V|Pairs]) :- 83 keys_values_pairs(Ks, Vs, Pairs). 84 85values_keys_pairs([], [], []). 86values_keys_pairs([V|Vs], [K|Ks], [K-V|Pairs]) :- 87 values_keys_pairs(Vs, Ks, Pairs). 88 89%! pairs_values(+Pairs, -Values) is det. 90% 91% Remove the keys from a list of Key-Value pairs. Same as 92% pairs_keys_values(Pairs, _, Values) 93 94pairs_values([], []). 95pairs_values([_-V|T0], [V|T]) :- 96 pairs_values(T0, T). 97 98 99%! pairs_keys(+Pairs, -Keys) is det. 100% 101% Remove the values from a list of Key-Value pairs. Same as 102% pairs_keys_values(Pairs, Keys, _) 103 104pairs_keys([], []). 105pairs_keys([K-_|T0], [K|T]) :- 106 pairs_keys(T0, T). 107 108 109%! group_pairs_by_key(+Pairs, -Joined:list(Key-Values)) is det. 110% 111% Group values with equivalent (==/2) consecutive keys. For 112% example: 113% 114% == 115% ?- group_pairs_by_key([a-2, a-1, b-4, a-3], X). 116% 117% X = [a-[2,1], b-[4], a-[3]] 118% == 119% 120% Sorting the list of pairs before grouping can be used to group 121% _all_ values associated with a key. For example, finding all 122% values associated with the largest key: 123% 124% == 125% ?- sort(1, @>=, [a-1, b-2, c-3, a-4, a-5, c-6], Ps), 126% group_pairs_by_key(Ps, [K-Vs|_]). 127% K = c, 128% Vs = [3, 6]. 129% == 130% 131% In this example, sorting by key only (first argument of sort/4 132% is 1) ensures that the order of the values in the original list 133% of pairs is maintained. 134% 135% @param Pairs Key-Value list 136% @param Joined List of Key-Group, where Group is the 137% list of Values associated with equivalent 138% consecutive Keys in the same order as they 139% appear in Pairs. 140 141group_pairs_by_key([], []). 142group_pairs_by_key([M-N|T0], [M-[N|TN]|T]) :- 143 same_key(M, T0, TN, T1), 144 group_pairs_by_key(T1, T). 145 146same_key(M0, [M-N|T0], [N|TN], T) :- 147 M0 == M, 148 !, 149 same_key(M, T0, TN, T). 150same_key(_, L, [], L). 151 152 153%! transpose_pairs(+Pairs, -Transposed) is det. 154% 155% Swap Key-Value to Value-Key. The resulting list is sorted using 156% keysort/2 on the new key. 157 158transpose_pairs(Pairs, Transposed) :- 159 flip_pairs(Pairs, Flipped), 160 keysort(Flipped, Transposed). 161 162flip_pairs([], []). 163flip_pairs([Key-Val|Pairs], [Val-Key|Flipped]) :- 164 flip_pairs(Pairs, Flipped). 165 166 167%! map_list_to_pairs(:Function, +List, -Keyed) 168% 169% Create a Key-Value list by mapping each element of List. 170% For example, if we have a list of lists we can create a 171% list of Length-List using 172% 173% == 174% map_list_to_pairs(length, ListOfLists, Pairs), 175% == 176 177:- meta_predicate 178 map_list_to_pairs(, , ). 179 180map_list_to_pairs(Function, List, Pairs) :- 181 map_list_to_pairs2(List, Function, Pairs). 182 183map_list_to_pairs2([], _, []). 184map_list_to_pairs2([H|T0], Pred, [K-H|T]) :- 185 call(Pred, H, K), 186 map_list_to_pairs2(T0, Pred, T)