This module implements common operations on Key-Value lists, also
known as Pairs. Pairs have great practical value, especially due
keysort/2 and the
This library is based on disussion in the SWI-Prolog mailinglist, including specifications from Quintus and a library proposal by Richard O'Keefe.
- [det]pairs_keys_values(?Pairs, ?Keys, ?Values)
- True if Keys holds the keys of Pairs and Values
Deterministic if any argument is instantiated to a finite list and the others are either free or finite lists. All three lists are in the same order.
- [det]pairs_values(+Pairs, -Values)
- Remove the keys from a list of Key-Value pairs. Same as
pairs_keys_values(Pairs, _, Values)
- [det]pairs_keys(+Pairs, -Keys)
- Remove the values from a list of Key-Value pairs. Same as
pairs_keys_values(Pairs, Keys, _)
- [det]group_pairs_by_key(+Pairs, -Joined:list(Key-Values))
- Group values with the same key. Pairs must be a key-sorted
list. For example:
?- group_pairs_by_key([a-2, a-1, b-4], X). X = [a-[2,1], b-]
Pairs Key-Value list, sorted to the standard order of terms (as keysort/2 does) Joined List of Key-Group, where Group is the list of Values associated with Key.
- [det]transpose_pairs(+Pairs, -Transposed)
- Swap Key-Value to Value-Key. The resulting list is sorted using keysort/2 on the new key.
- map_list_to_pairs(:Function, +List, -Keyed)
- Create a Key-Value list by mapping each element of List. For
example, if we have a list of lists we can create a list of Length-List
map_list_to_pairs(length, ListOfLists, Pairs),