Function Card(Identifier, Suffix)

Card

The function Card returns the cardinality of an identifier, or the cardinality of a suffix of that identifier. To support the various usages there are three different flavors of Card:

Card(
    Identifier    ! (input) a set expression
    )

Card(
    Identifier    ! (input) an identifier reference
    )

Card(
    Identifier,    ! (input) element in the set AllIdentifiers
    [Suffix]       ! (optional) element in the set AllSuffixNames
    )

Arguments

Identifier

A reference to an identifier that may contain data, or a simple set or a set expression.

Suffix

An element in the predefined set of AllSuffixNames.

Return Value

If the first argument is a set (expression), the function will return the number of elements in the set. In all other cases the function returns the number of nondefault values stored in the data of the given identifier, or in the data of the suffix of that identifier.

Example

! Some data
_s_genders := data { male, female };
_s_names := data { John, Jill, Jack, Joan } ;
_s_nameByGender(_i_gender) := data {
        male : { John, Jack },
        female : { Jill, Joan }
} ;

! Getting the cardinality of a set
_p_noGenders := card(_s_genders); ! Returns 2
_p_noNames := card( _s_names );  ! Returns 4

! Getting the cardinality of sets in an indexed set
_p_noNamesByGender(_i_gender) :=
        card( _s_nameByGender( _i_gender ) ); ! Returns 2, twice.

Note

• The Card function cannot be applied to slices of indexed identifiers. In such a case, you can use the Count operator to count the number of nondefault elements.

• When the Card function is used inside the definition of a parameter or a set and the first argument is an index or element parameter into the set AllIdentifiers (using the third prototype above) then the definition depends on all identifiers that can appear on the left hand side of an assignment (sets without a definition, parameters without a definition, variables and constraints). The cardinality will be computed for all identifiers, including those with a definition. These definitions will not be made up to date, however. This is illustrated in the following example.

  Parameter A;
  Parameter B {
      Definition   :  A + 1;
  }
  Parameter TheCards {
      IndexDomain  :  IndexIdentifiers;
      Definition   :  Card( IndexIdentifiers, 'Level' );
  }
  Body:
      A := 1;
      display TheCards;
  

  Here TheCards is computed in the display statement because A just changed. The definition of TheCards, that is made up to date by the display statement, will, however, not invoke the computation of B, although it is not up to date. This is done in order to avoid circular references while making set and parameter definitions up to date. In order to make B up to date consider using the Update statement, see also Nonprocedural Execution of the Language Reference.

See also

The function ActiveCard and the Count operator (see also Nonprocedural Execution of the Language Reference).