Optional parameters
You are encouraged to solve this task according to the task description, using any language you may know.
Define a function/method/subroutine which sorts a sequence ("table") of sequences ("rows") of strings ("cells"), by one of the strings. Besides the input to be sorted, it shall have the following optional parameters:
- ordering
- A function specifying the ordering of strings; lexicographic by default.
- column
- An integer specifying which string of each row to compare; the first by default.
- reverse
- Reverses the ordering.
This task should be considered to include both positional and named optional parameters, as well as overloading on argument count as in Java or selector name as in Smalltalk, or, in the extreme, using different function names. Provide these variations of sorting in whatever way is most natural to your language.
Do not implement a sorting algorithm; this task is about the interface. If you can't use a built-in sort routine, just omit the implementation (with a comment).
Common Lisp
Common Lisp has both named and positional parameters.
<lang lisp> (defun sort-table (table &key (ordering #'string<)
(column 0)
reverse)
(sort table (if reverse
(complement ordering)
ordering)
:key (lambda (row) (elt row column))))</lang>
(Notes: The builtin sort takes a "less than" predicate function. The complement function inverts a predicate.)
Example uses: <lang lisp>CL-USER> (defparameter *data* '(("a" "b" "c") ("" "q" "z") ("zap" "zip" "Zot")))
- DATA*
CL-USER> (sort-table *data*) (("" "q" "z") ("a" "b" "c") ("zap" "zip" "Zot"))
CL-USER> (sort-table *data* :column 2) (("zap" "zip" "Zot") ("a" "b" "c") ("" "q" "z"))
CL-USER> (sort-table *data* :column 1) (("a" "b" "c") ("" "q" "z") ("zap" "zip" "Zot"))
CL-USER> (sort-table *data* :column 1 :reverse t) (("zap" "zip" "Zot") ("" "q" "z") ("a" "b" "c"))
CL-USER> (sort-table *data* :ordering (lambda (a b) (> (length a) (length b)))) (("zap" "zip" "Zot") ("a" "b" "c") ("" "q" "z"))</lang>
Fortran
In Fortran, each argument has its "name". The optional attribute can be used to specify that an argument is optional, and its presence (or absence) can be tested using the present intrinsic (so that we can give a default value, or execute accordingly a totally different code).
<lang fortran>module ExampleOptionalParameter
! use any module needed for the sort function(s) ! and all the interfaces needed to make the code work implicit none
contains
subroutine sort_table(table, ordering, column, reverse)
type(table_type), intent(inout) :: table
integer, optional :: column
logical, optional :: reverse
optional :: ordering
interface
integer function ordering(a, b)
type(table_element), intent(in) :: a, b
end function ordering
end interface
integer :: the_column, i logical :: reversing type(table_row) :: rowA, rowB
if ( present(column) ) then
if ( column > get_num_of_columns(table) ) then
! raise an error?
else
the_column = column
end if
else
the_column = 1 ! a default value, de facto
end if
reversing = .false. ! default value if ( present(reverse) ) reversing = reverse
do
! loops over the rows to sort... at some point, we need
! comparing an element (cell) of the row, with the element
! in another row; ... let us suppose rowA and rowB are
! the two rows we are considering
ea = get_element(rowA, the_column)
eb = get_element(rowB, the_column)
if ( present(ordering) ) then
if ( .not. reversing ) then
if ( ordering(ea, eb) > 0 ) then
! swap the rowA with the rowB
end if
else ! < instead of >
if ( ordering(ea, eb) < 0 ) then
! swap the rowA with the rowB
end if
end if
else
if ( .not. reversing ) then
if ( lexinternal(ea, eb) > 0 ) then
! swap the rowA with the rowB
end if
else ! < instead of >
if ( lexinternal(ea, eb) < 0 ) then
! swap the rowA with the rowB
end if
end if
end if
! ... more of the sorting algo ...
! ... and rows traversing ... (and an exit condition of course!)
end do
end subroutine sort_table
end module ExampleOptionalParameter</lang>
<lang fortran>program UsingTest
use ExampleOptionalParameter implicit none
type(table_type) :: table
! create the table...
! sorting taking from column 1, not reversed, using internal ! default comparator call sort_table(table)
! the same as above, but in reversed order; we MUST specify ! the name of the argument since it is not given in the same ! order of the subroutine spec call sort_table(table, reverse=.true.)
! sort the table using a custom comparator call sort_table(table, my_cmp) ! or call sort_table(table, ordering=my_cmp)
! as above, but taking from column 2 call sort_table(table, my_cmp, 2) ! or (swapping the order of args for fun) call sort_table(table, column=2, ordering=my_cmp)
! with custom comparator, column 2 and reversing... call sort_table(table, my_cmp, 2, .true.) ! of course we can swap the order of optional args ! by prefixing them with the name of the arg
! sort from column 2, with internal comparator call sort_table(table, column=2)
end program UsingTest</lang>
Java
Java has no optional parameters, but methods can be overloaded on the number and types of arguments, which can be used to effectively achieve optional positional parameters.
<lang java>import java.util.*;
// the "natural ordering" comparator // taken from Apache Commons Collections class ComparableComparator<T extends Comparable<? super T>>
implements Comparator<T> {
public int compare(T a, T b) {
return a.compareTo(b);
}
}
public class OptionalParams {
public static <T extends Comparable<? super T>> void
sortTable(T[][] table) {
sortTable(table, 0);
}
public static <T extends Comparable<? super T>> void
sortTable(T[][] table,
int column) {
sortTable(table, column, false);
}
public static <T extends Comparable<? super T>> void
sortTable(T[][] table,
int column, boolean reverse) {
sortTable(table, column, reverse, new ComparableComparator<T>());
}
public static <T> void sortTable(T[][] table,
final int column,
final boolean reverse,
final Comparator<T> ordering) {
Comparator<T[]> myCmp = new Comparator<T[]>() {
public int compare(T[] x, T[] y) {
return (reverse ? -1 : 1) *
ordering.compare(x[column], y[column]);
}
};
Arrays.sort(table, myCmp);
}
public static void main(String[] args) {
String[][] data0 = {{"a", "b", "c"},
{"", "q", "z"},
{"zap", "zip", "Zot"}};
System.out.println(Arrays.deepToString(data0));
// prints: [[a, b, c], [, q, z], [zap, zip, Zot]]
// we copy it so that we don't change the original copy
String[][] data = data0.clone();
sortTable(data);
System.out.println(Arrays.deepToString(data));
// prints: [[, q, z], [a, b, c], [zap, zip, Zot]]
data = data0.clone();
sortTable(data, 2);
System.out.println(Arrays.deepToString(data));
// prints: [[zap, zip, Zot], [a, b, c], [, q, z]]
data = data0.clone();
sortTable(data, 1);
System.out.println(Arrays.deepToString(data));
// prints: [[a, b, c], [, q, z], [zap, zip, Zot]]
data = data0.clone();
sortTable(data, 1, true);
System.out.println(Arrays.deepToString(data));
// prints: [[zap, zip, Zot], [, q, z], [a, b, c]]
data = data0.clone();
sortTable(data, 0, false, new Comparator<String>() {
public int compare(String a, String b) {
return b.length() - a.length();
}
});
System.out.println(Arrays.deepToString(data));
// prints: [[zap, zip, Zot], [a, b, c], [, q, z]]
}
}</lang>
OCaml
OCaml has optional named parameters. It is conventional to place a non-optional parameter after the optional parameters, because if the optional parameters were at the end, then if you don't provide them, it will just look like a partial application (because OCaml supports currying), resulting in a function which still expects the optional parameters.
<lang ocaml>let sort_table ?(ordering = compare) ?(column = 0) ?(reverse = false) table =
let cmp x y = ordering (List.nth x column) (List.nth y column) * (if reverse then -1 else 1) in List.sort cmp table</lang>
Example uses: <lang ocaml># let data = [["a"; "b"; "c"]; [""; "q"; "z"]; ["zap"; "zip"; "Zot"]];; val data : string list list =
[["a"; "b"; "c"]; [""; "q"; "z"]; ["zap"; "zip"; "Zot"]]
- sort_table data;;
- : string list list = [[""; "q"; "z"]; ["a"; "b"; "c"]; ["zap"; "zip"; "Zot"]]
- sort_table ~column:2 data;;
- : string list list = [["zap"; "zip"; "Zot"]; ["a"; "b"; "c"]; [""; "q"; "z"]]
- sort_table ~column:1 data;;
- : string list list = [["a"; "b"; "c"]; [""; "q"; "z"]; ["zap"; "zip"; "Zot"]]
- sort_table ~column:1 ~reverse:true data;;
- : string list list = [["zap"; "zip"; "Zot"]; [""; "q"; "z"]; ["a"; "b"; "c"]]
- sort_table ~ordering:(fun a b -> compare (String.length b) (String.length a)) data;;
- : string list list = [["zap"; "zip"; "Zot"]; ["a"; "b"; "c"]; [""; "q"; "z"]]</lang>
OCaml does not support optional positional parameters, because, since OCaml supports currying, it would conflict with partial applications, where you do not provide all the arguments to a function, and it results in a function which expects the remaining arguments.
Python
only (the "cmp" argument to sorted() is no longer accepted in Python 3)
Using a pretty-printer for the table <lang python>>>> def printtable(data):
for row in data:
print ' '.join('%-5s' % ('"%s"' % cell) for cell in row)
>>> def sorttable(table, ordering=None, column=0, reverse=False):
return sorted(table, cmp=ordering, key=lambda row: row[column], reverse=reverse)
>>> data = [["a", "b", "c"], ["", "q", "z"], ["zap", "zip", "Zot"]] >>> printtable(data) "a" "b" "c" "" "q" "z" "zap" "zip" "Zot" >>> printtable( sorttable(data) ) "" "q" "z" "a" "b" "c" "zap" "zip" "Zot" >>> printtable( sorttable(data, column=2) ) "zap" "zip" "Zot" "a" "b" "c" "" "q" "z" >>> printtable( sorttable(data, column=1) ) "a" "b" "c" "" "q" "z" "zap" "zip" "Zot" >>> printtable( sorttable(data, column=1, reverse=True) ) "zap" "zip" "Zot" "" "q" "z" "a" "b" "c" >>> printtable( sorttable(data, ordering=lambda a,b: cmp(len(b),len(a))) ) "zap" "zip" "Zot" "a" "b" "c" "" "q" "z" >>> </lang>
Tcl
In Tcl, optional arguments are collected when the last argument to a proc definition is called "args". The lsort command has a similar API, but with different keywords, so we adapt them.
By convention, optional parameter names in Tcl start with a leading “-” character. <lang Tcl>package require Tcl 8.5
proc tablesort {table args} {
array set opt {-ordering "" -column 0 -reverse 0}
array set opt $args
set pars [list -index $opt(-column)]
if {$opt(-reverse)} {lappend pars -decreasing}
if {$opt(-ordering) ne ""} {lappend pars -command $opt(-ordering)}
lsort {*}$pars $table
}
puts [tablesort $data]
- --> {"" q z} {a b c} {zap zip Zot}
puts [tablesort $data -column 1]
- --> {a b c} {"" q z} {zap zip Zot}
puts [tablesort $data -column 0]
- --> {"" q z} {a b c} {zap zip Zot}
puts [tablesort $data -column 0 -reverse 1]
- --> {zap zip Zot} {a b c} {"" q z}
puts [tablesort $data -ordering {
apply {{a b} {expr {[string length $b]-[string length $a]}}}
}]
- --> {zap zip Zot} {a b c} {"" q z}</lang>