Prolog - formulate query that finds highest value within a finite amount of atoms?

Question

Suppose I had an atom name and age pair:

person(bob,42).
person(jeff,12).
person(adam,23).
...

And I wanted to find through a query (not predicate) the youngest person.

How would I make such a query?

See [this question and answers](http://stackoverflow.com/questions/27317069/collect-all-minimum-solutions-from-a-backtrackable-predicate). By the way, what is the difference between a query and a predicate? If you just take the body of a predicate, it would be the query, I guess? — , Nov 07 '15 at 08:52

score 1 · Answer 1 · answered Nov 06 '15 at 16:24

You can formulate a multi-part query with a universal quantifier, like this:

person(X,AgeX), forall(person(Y,AgeY), X=Y;AgeX<AgeY).

Essentially, this query says that X must be such that for each known person Y in the database it should either be the same person (X=Y part) or the other person must be older (AgeX<AgeY part)

Demo.

score 0 · Answer 2 · answered Nov 06 '15 at 19:32

0

library(aggregate) solves such task, and much more... try

?- aggregate(min(Age,Person), person(Person,Age), R).
R = min(12, jeff).

answered Nov 06 '15 at 19:32

CapelliC

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Prolog - formulate query that finds highest value within a finite amount of atoms?

2 Answers2