find minimum of list inside list on the basis of one value

Question

I have this list in prolog

[[[dublin, london], 1000], [[dublin, moscow, london], 5000]]

And I want to calculate the minimum of the list such that answer should be

[[dublin, london], 1000]

This question has some similar problem minimum in list of lists in prolog

But that doesn't seems to working I am getting output as false. Please help

Answer 1

Try library(aggregate):

?- aggregate_all(min(X,Y), 
       member([Y,X], [[[dublin, london], 1000], 
                      [[dublin, moscow, london], 5000]]), 
       R).
R = min(1000, [dublin, london]).

See also here:

Aggregation operators on backtrackable predicates
https://www.swi-prolog.org/pldoc/man?section=aggregate