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Set modifiers with implicit field value definitions

The following describes how to define a set of field values using a nested set definition.

In such cases, the element functions P() and E() must be used, representing the element set of possible values and the excluded values of a field, respectively. Inside the parentheses, it is possible to specify one set expression and one field, for example P({1} Customer). These functions cannot be used in other expressions.

Note: The element functions, P() and E(), can only be used on a natural set. That is, a set of records that can be defined by a simple selection. For example, the set given by {1-$} cannot be always be defined through selection, and is therefore, not a natural set. Using these functions on non-natural sets can give rise to unexpected results.

Examples and results:  

Examples Results
sum( {$<Customer = P({1<Product={‘Shoe’}>} Customer)>} Sales )

Returns the sales for current selection, but only those customers that ever have bought the product ‘Shoe’. The element function P( ) here returns a list of possible customers; those that are implied by the selection ‘Shoe’ in the field Product.
sum( {$<Customer = P({1<Product={‘Shoe’}>})>} Sales )

Same as above. If the field in the element function is omitted, the function will return the possible values of the field specified in the outer assignment.
sum( {$<Customer = P({1<Product={‘Shoe’}>} Supplier)>} Sales )

Returns the sales for current selection, but only those customers that ever have supplied the product ‘Shoe’. The element function P( ) here returns a list of possible suppliers; those that are implied by the selection ‘Shoe’ in the field Product. The list of suppliers is then used as a selection in the field Customer.
sum( {$<Customer = E({1<Product={‘Shoe’}>})>} Sales )

Returns the sales for current selection, but only those customers that never bought the product ‘Shoe’. The element function E( ) here returns the list of excluded customers; those that are excluded by the selection ‘Shoe’ in the field Product.