Builtin predicates - Sorting
Predicates in this group are used to efficiently sort lists into ascending or descending order. The sorting algorithm used is merge sort, which provides a stable sort where elements with the same key keep their relative ordering in the result.
keysort/2, keysortd/2, msort/2, msortd/2, rkeysort/2, rkeysortd/2, sort/2, sortd/2
keysort/2 - sorts a keyed list into ascending order.
- Usage
- keysort(List, Sorted)
- Description
- Unifies Sorted with a sorted version of List. The elements should be functors of arity 2. The first argument to the functor is used as a key to be ordered according to (@<)/2. The tail of List can be a variable; the sorted version will have nil as its tail.
- If an element is not a functor of arity 2, then the element itself will be used as the key.
- Errors
instantiation_error - List is a variable. type_error(list, List) - List is not a list or the tail of List is not nil or a variable.
- Examples
keysort([a - 1, y - 2, b - 8, m - 6], [a - 1, b - 8, m - 6, y - 2])
- Compatibility
- SWI-Prolog has a keysort/2 predicate that performs the same function as this predicate with some minor changes. Plang supports any arity-2 functor for the element (or no arity-2 functor) whereas SWI-Prolog mandates the use of (-)/2. Plang's version is backwards compatible with SWI-Prolog's.
- See Also
- (@<)/2, keysortd/2, rkeysort/2, sort/2
keysortd/2 - sorts a keyed list into descending order.
- Usage
- keysortd(List, Sorted)
- Description
- Unifies Sorted with a sorted version of List. The elements should be functors of arity 2. The first argument to the functor is used as a key to be ordered according to (@>)/2. The tail of List can be a variable; the sorted version will have nil as its tail.
- If an element is not a functor of arity 2, then the element itself will be used as the key.
- Errors
instantiation_error - List is a variable. type_error(list, List) - List is not a list or the tail of List is not nil or a variable.
- Examples
keysortd([a - 1, y - 2, b - 8, m - 6], [y - 2, m - 6, b - 8, a - 1])
- See Also
- (@>)/2, keysort/2, rkeysortd/2, sortd/2
msort/2 - sorts a list into ascending order without removing duplicates.
- Usage
- msort(List, Sorted)
- Description
- Unifies Sorted with a sorted version of List. The elements are ordered according to (@<)/2. The tail of List can be a variable; the sorted version will have nil as its tail.
- Errors
instantiation_error - List is a variable. type_error(list, List) - List is not a list or the tail of List is not nil or a variable.
- Examples
msort([a, y, b, m], [a, b, m, y])
msort([a, y, a, m], [a, a, m, y])
- Compatibility
- SWI-Prolog
- See Also
- (@<)/2, keysort/2, msortd/2, sort/2
msortd/2 - sorts a list into descending order without removing duplicates.
- Usage
- msortd(List, Sorted)
- Description
- Unifies Sorted with a sorted version of List. The elements are ordered according to (@>)/2. The tail of List can be a variable; the sorted version will have nil as its tail.
- Errors
instantiation_error - List is a variable. type_error(list, List) - List is not a list or the tail of List is not nil or a variable.
- Examples
msortd([a, y, b, m], [y, m, b, a])
msortd([a, y, a, m], [y, m, a, a])
- See Also
- (@>)/2, keysortd/2, msort/2, sortd/2
rkeysort/2 - sorts a keyed list into ascending order with reversed keying.
- Usage
- rkeysort(List, Sorted)
- Description
- Unifies Sorted with a sorted version of List. The elements should be functors of arity 2. The second argument to the functor is used as a key to be ordered according to (@<)/2. The tail of List can be a variable; the sorted version will have nil as its tail.
- If an element is not a functor of arity 2, then the element itself will be used as the key.
- Errors
instantiation_error - List is a variable. type_error(list, List) - List is not a list or the tail of List is not nil or a variable.
- Examples
rkeysort([a - 1, y - 2, b - 8, m - 6], [a - 1, y - 2, m - 6, b - 8])
- See Also
- (@<)/2, keysortd/2, rkeysort/2, sort/2
rkeysortd/2 - sorts a keyed list into descending order with reversed keying.
- Usage
- rkeysortd(List, Sorted)
- Description
- Unifies Sorted with a sorted version of List. The elements should be functors of arity 2. The second argument to the functor is used as a key to be ordered according to (@>)/2. The tail of List can be a variable; the sorted version will have nil as its tail.
- If an element is not a functor of arity 2, then the element itself will be used as the key.
- Errors
instantiation_error - List is a variable. type_error(list, List) - List is not a list or the tail of List is not nil or a variable.
- Examples
rkeysortd([a - 1, y - 2, b - 8, m - 6], [b - 8, m - 6, y - 2, a - 1])
- See Also
- (@>)/2, keysortd/2, rkeysort/2, sortd/2
sort/2 - sorts a list into ascending order and remove duplicates.
- Usage
- sort(List, Sorted)
- Description
- Unifies Sorted with a sorted version of List. The elements are ordered according to (@<)/2. The tail of List can be a variable; the sorted version will have nil as its tail. Duplicate elements in List will appear only once in Sorted
- Errors
instantiation_error - List is a variable. type_error(list, List) - List is not a list or the tail of List is not nil or a variable.
- Examples
sort([a, y, b, m], [a, b, m, y])
sort([a, y, a, m], [a, m, y])
- Compatibility
- SWI-Prolog
- See Also
- (@<)/2, keysort/2, msort/2, sortd/2
sortd/2 - sorts a list into descending order and remove duplicates.
- Usage
- sortd(List, Sorted)
- Description
- Unifies Sorted with a sorted version of List. The elements are ordered according to (@>)/2. The tail of List can be a variable; the sorted version will have nil as its tail. Duplicate elements in List will appear only once in Sorted
- Errors
instantiation_error - List is a variable. type_error(list, List) - List is not a list or the tail of List is not nil or a variable.
- Examples
sortd([a, y, b, m], [y, m, b, a])
sortd([a, y, a, m], [y, m, a])
- See Also
- (@>)/2, keysortd/2, msortd/2, sort/2
