From m204wiki
Jump to navigation Jump to search

Conditionally add an item to a $list

Note: Many $functions have been deprecated in favor of Object Oriented methods. The OO equivalent for the $List_Add_Unique function is AddUnique.

This function adds an item to a $list if an identical item isn't already there, adding the item to the end of the $list.

$List_Add_Unique is a callable $function.


[%RC =] $List_Add_Unique(list, string)

Syntax terms

%rc A numeric variable that is the item number of the added string, or it is the negative of the item number that exactly matches the string being added.
list The $list identifier of the $list to which the string is to be added. This is a required argument.
string The string to add to the $list. This is a required argument.

Usage notes

  • All errors in $List_Add_Unique result in request cancellation.
  • $List_Add_Unique always adds the indicated string to the end of the $list but does not add it if there's already an identical $list item on the $list. $List_Add_Unique does not assume any order for the $list so sequentially scans the entire $list for matches to the string being added. Because of this, it will generally be more expensive to use than $List_Add_Unique_Ordered for very large $lists though this latter function might not be usable in all cases — say, if the target $list starts out unordered.
  • $List_Add_Unique returns the either the item number added if no match was found or the negative item number of the matching item if one was found. This return code makes it easy to maintain a parallel $list that contains say a count of the number of times a given value occurred, that is was passed as a string to $List_Add_Unique. The following illustrates such an approach:

    %IN = $List_Add_Unique(%OLIST, %DATA) IF %IN GT 0 THEN %RC = $ListIns(%CLIST, %IN, 1) ELSE %IN = -%IN %RC = $ListRep(%CLIST, %IN, $ListInf(%CLIST, %IN) +1 ) END IF

Products authorizing $List_Add_Unique