# Remove elements from a set¶

This article explains the possible behaviors of the empty statement.

To remove all the elements from a set, you can use the empty statement in AIMMS.

The behavior of the empty statement depends on the set that you provide as an argument:

• The set is not a subset of AllIdentifiers -
The empty statement will remove all elements from the given set.
• The set is a subset of AllIdentifiers -
The empty statement will empty all the identifiers that are in the given subset.

Let’s assume the following two identifiers:

SET:
identifier :  NormalSet

SET:
identifier :  ActiveVariables
subset of  :  AllVariables


As you can see, it holds that ActiveVariables $$\subseteq$$ AllVariables $$\subseteq$$ AllIdentifiers because the predefined set AllVariables is defined in AIMMS to be a subset of AllVariablesConstraints, which in turn is a subset of AllIdentifiers. You can verify this by opening the attribute window of these predefined sets.

This means that the empty statement behaves differently for NormalSet and ActiveVariables, as explained below:

!This will remove all elements from the set NormalSet
empty NormalSet ;

!This will clear the values of all variables in the subset ActiveVariables
!After the empty statement, the set itself will still contain elements!
empty ActiveVariables ;

!This will actually remove all elements from the set ActiveVariables
ActiveVariables := {} ;


Last Updated: July, 2019