Entity

public abstract class Entity<T>

An AMPL entity such as a parameter or a variable. An entity can either represent a single instance of an AMPL algebraic entity or, if the corresponding declaration has an indexing expression, a mapping from keys to instances. In the derived classes, it has methods to access instance-level properties which can be used in case the represented entity is scalar. To gain access to all the values in an entity (for all instances and all suffixes for that entities), use getValues.

Methods

public Set<Map.Entry<Object, T>> entrySet()

Get a set view of this entity. Each entry in the set contains the key (value of the indices) and the corresponding instance. For a scalar entity, a set with just one entry is returned, which has a null key and the only instance as value.

The following example prints indices and values of the variable Buy indexed over the set FOOD (taken from the diet model):

for(Map.Entry<Object, VariableInstance> e: ampl.getVariable("Buy").entrySet()) {
        Object food = e.getKey();
        VariableInstance buy = e.getValue();
        System.out.format("%s %g%n", food, buy.value());
}
Returns:An unmodifiable set containing all the entries of this entity.
public abstract T get()

Get the instance corresponding to a scalar entity.

Throws:
Returns:

The corresponding instance.
public abstract T get(Object... key)

Get the instance corresponding to the specified key. See Access to instances and values for further information on how the key can be specified.

Parameters:
  • key – Key of the instance to be found.
Throws:
Returns:

The instance corresponding to the key, or null if the specified key is not found.
public abstract T get(Tuple key)

Get the instance corresponding to the specified tuple. See Access to instances and values for further information on how the key can be specified.

Parameters:
  • key – Key (in form of Tuple) of the instance to be found.
Throws:
Returns:

The instance corresponding to the key, or null if the specified key is not found.
public String[] getIndexingSets()

Get the AMPL string representation of the sets on which this entity is indexed.

Returns:The string representation of the indexing sets for this entity or an empty array if the entity is scalar
public Set<Object> getIndices()

Get all the keys in this entity. Not modifiable as a collection.

Returns:All the keys currently in the entity.
public Collection<T> getInstances()

Get all instances in this entity. Not modifiable as a collection

Returns:All instances currently generated for this entity.
public DataFrame getValues()

Get the principal values of this entity as a DataFrame. For variables and objectives it returns their suffix val for parameters it returns their values for constraints it returns the suffix dual for sets it returns all the members of the set

Returns:All instances
public DataFrame getValues(String... suffixes)

Get all the specified values for this entity as a DataFrame object. The valid strings are all AMPL built-in suffixes for the entity under consideration.

Parameters:
  • suffixes – A list of suffixes to be returned
Throws:
Returns:

A DataFrame object with a column for each indexing set and a column for each one of the specified suffixes.
public boolean hasIndexing()

Check whether this entity is indexed over any set. Equivalent to testing whether Entity.indexarity is greater than zero.

Returns:True if the entity is not scalar (is indexed over a set)
public int indexarity()

Get the indexarity of this entity (sum of the dimensions of the indexing sets). This value indicates how many elements are to be passed to the method Entity.get in order to access an instance of this entity.

See the following AMPL examples:

var x;               # indexarity = 0
var y {1..2};        # indexarity = 1
var z {1..2,3..4};   # indexarity = 2
var zz {{(1, 2)}};   # indexarity = 2
Returns:The sum of the dimensions of the indexing sets or 0 if the entity is not indexed
public boolean isScalar()

Check whether this entity is scalar. Equivalent to testing whether Entity.indexarity is equal to zero.

Returns:True if the entity is scalar (not indexed over any set)
public final String name()

Get the AMPL name of this entity

public int numInstances()

Get the number of instances in this entity

public String toString()

Get a string representation of this entity; for all entity types, it returns the AMPL declaration.

public List<Entity<?>> xref()

Get all the entities which depend on this one