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This function determines the intersection of two collections. It returns a collection containing the items that are present in both specified collections.

Syntax

Code Block
INTERSECTION ( collection1 , collection2 )
  • collection1, collection2 - Collections to be intersected. These collections must be of the same base type.

Return type

  • collection

Examples

Suppose the following model. Entity Teacher has a multivalued relation with entity Child via the relation Teacher.teaches_Children.

 

Teacher instanceChild instanceChild.nameChild.hobbies
Teacher_1Child_1“Kim”“Reading”, “Dancing”
Teacher_1Child_2“Rick”“Tennis”, “Dancing”
Teacher_1Child_3“Bob”“Painting”, “Basketball”, “Reading”
Teacher_2Child_1“Kim”“Reading”, “Dancing”
Teacher_2Child_3“Bob”“Painting”, “Basketball”, “Reading”
Teacher_2Child_4“Mary”“Football”

 

  • INTERSECTION ( Teacher[Teacher_1].teaches_Children , Teacher[Teacher_2].teaches_Children ) results in a collection of Child instances Child_1 and Child_3
  • INTERSECTION ( Teacher[Teacher_1].teaches_Children.name , Teacher[Teacher_2].teaches_Children.name ) = “Kim”, “Bob”
  • INTERSECTION ( Child[Child_1].hobbies , Child[Child_3].hobbies ) = “Reading”
  • INTERSECTION ( Child[Child_2].hobbies , Child[Child_3].hobbies ) results in an empty list

DIFFERENCE

This function returns a collection containing all the items from collection1 that are not present in collection 2.

Syntax

Code Block
DIFFERENCE ( collection1 , collection2 )
  • collection1, collection2 - Collections to be intersected. These collections must be of the same base type.

Return type

  • collection

Examples

  • DIFFERENCE (
Teacher[Teacher_1].teaches_Children , Teacher[Teacher_2].teaches_Children ) results in a collection of Child instances Child_1 and Child_3
  • DIFFERENCE ( Teacher[Teacher_1].teaches_Children.name , Teacher[Teacher_2].teaches_Children.name ) = “Kim”, “Bob”
  • DIFFERENCE ( Child[Child_1].hobbies , Child[Child_3].hobbies ) = “Reading”
    • [ "a", "b", "c"] , [ "c", "d", "e" ] ) = [ "a" , "b" ]
    • DIFFERENCE ( [ "nv" , "bv" ] , [ "NV" ] ) = [ "bv" ]
    • DIFFERENCE ( 1 , 1
    DIFFERENCE ( Child[Child_2].hobbies , Child[Child_3].hobbies
    • ) results in an empty list

    SYMMETRIC_DIFFERENCE

    This function determines the symmetric difference between two collections. It returns a collection with the elements of the provided collections which are in either one of the collections, but not in both.

    Syntax

    Code Block
    SYMMETRIC_DIFFERENCE ( collection1 , collection2 )
    • collection1, collection2 - Collections to be intersected. These collections must be of the same base type.

    Return type

    • collection

    Examples

    • SYMMETRIC_DIFFERENCE ( [ "a", "b", "c"] , [ "c", "d", "e" ] ) = [ "a", "b", "d", "e" ]
    • SYMMETRIC_DIFFERENCE ( [ "nv" , "bv" ] , [ "NV" ] ) = [ "bv" ]
    • SYMMETRIC_DIFFERENCE ( 1 , 1 ) results in an empty list

    Collections vs. lists

    UNIQUE, SUBSET, UNION and INTERSECTION return a collection of data, i.e. double entries are removed. However, COLLECT statements, + and - return a list of data. You have to be aware of this when using the SIZE or UNPACK function.

    Example

    Statuses = ["a","b","c","d","a","b","c","d"].

    Result

    The expression "SIZE ( COLLECT Status FROM {Statuses} )" will result in 8. Note that duplicates are not removed.

    The expression "SIZE ( UNIQUE ( COLLECT Status FROM {Statuses} ) )" will result in 4, as the unique filters the duplicates.

    UI Text Box
    typewarning

    When the expression is completely evaluated, all duplicates are filtered as well. Using COLLECT Status FROM {Statuses} as a default expression on an attribute, will result in 4 elements.