When working with subsets of indexes, you sometimes want to create new indexes based on previous ones. MPL allows you to use standard set operations such as difference, not, union, and intersection to help define new indexes.
The set difference operation is specified by using the minus (-) symbol between two indexes. It will subtract from the first index all the elements that are in the second index and create a new index containing the remaining elements.
The not operation on index is specified by placing the keyword NOT in front of the index. It will select all the elements from the parent index that are not defined in the given index.
The set union operation can be specified by placing either the plus symbol (+), the OR keyword or the UNION keyword between two indexes. It merges all the elements from both of the indexes into one large index.
The set intersection operation is specified by placing either the AND keyword or the INTERSECTION keyword between two indexes. It creates a new index that contains only the elements that are defined in both of the indexes.
Example of set operations:
INDEX
plants := (NewYork, Chicago, London, Paris);
OpenPlants[plants] := (NewYork, London);
EuropePlants[plants] := (London, Paris);
! Difference
ClosedPlants[plants] := plants - OpenPlants;
:= (Chicago, Paris)
! Not
USPlants[plants] := NOT EuropePlants;
:= (NewYork, Chicago)
! Union
OpenOrEurope[plants] := OpenPlants OR EuropePlants;
:= (NewYork, London, Paris)
! Intersection
OpenAndEurope[plants] := OpenPlants AND EuropePlants;
:= (London)