sort(+Key, +Order, +Random, ?Sorted)

+Key

A non-negative integer or a list of positive integers.

+Order

One of the atoms <, =<, > or >=.

+Random

List.

?Sorted

List or variable.

Description

If Random is not a list of compound terms, use Key = 0.

If Random is a list of compound terms, then the sort will be according to the Keyth argument of the first element of the lists. If Key = 0, then the sort is on the entire terms.

In all cases, Order specifies whether the list is sorted into ascending (<, =<) or descending (>, >=) order and whether duplicates are to be retained (=<, >=) or eliminated (<, >). The way to remember the Order argument is that it is the relation which holds between adjacent elements in the result.

The sort is done according to the standard ordering of terms. See compare/3 for the definition of this standard ordering.

Fail Conditions

Resatisfiable

Exceptions

(5) type error

Key is greater than 0, and one of List1 and List2 does not have all elements compound terms.

(5) type error

Key is not an integer or a list of integers.

(6) out of range

One of the compound terms in List1 or List2 has not got as many as Key arguments.

Examples

Success:
      sort(0,<,[3,1,6,7,2],S).     (gives S=[1,2,3,6,7]).
      sort(0,>,[q,1,3,a,e,N],S).
                           (gives N=_g78,S=[q,e,a,3,1,_g78]).
      sort(0,=<,[1,3,2,3,4,1],S).  (gives S=[1,1,2,3,3,4]).
      sort(2,<,[f(1,3),h(2,1)],S). (gives S=[h(2,1),f(1,3)]).
      sort(1,<,[f(1,3),h(2,1)],S). (gives S=[f(1,3),h(2,1)]).
      sort([2,1],=<,[f(3,a(2)),f(1,a(1)),f(0,a(3)),f(1,a(4))],S).
                           (gives S=[f(1,a(1)),f(3,a(2)),f(0,a(3)),f(1,a(4))]).

Fail:
      sort(0,<,[2,1,3,4],[2,1,3,4]).

Error:
      sort(1,<,[f(1),f(3),5],S).        (Error 5).
      sort(1.0,<,[f(1),f(3),f(5)],S).   (Error 5).
      sort(2,<,[f(1,2),g(3,a),f(5)],S). (Error 6).

See Also