EquivalenceSet (Apache Calcite API)

java.lang.Object
- org.apache.calcite.util.EquivalenceSet<E>

Type Parameters:

E - Element type
```
public class EquivalenceSet<E extends java.lang.Comparable<E>>
extends java.lang.Object
```
Set of elements organized into equivalence classes.
Elements are equivalent by the rules of a mathematical equivalence relation:

Reflexive
Every element e is equivalent to itself
Symmetric
If e is equivalent to f, then f is equivalent to e
Transitive
If e is equivalent to f, and f is equivalent to g, then e is equivalent to g

For any given pair of elements, answers in O(log N) (two hash-table lookups) whether they are equivalent to each other.

Field Summary

Fields
Modifier and Type Field Description

private java.util.Map<E,E> parents

Constructor Summary

Constructors
Constructor Description

EquivalenceSet()

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`E`	`add(E e)`	Adds an element, and returns the element (which is its own parent).
`boolean`	`areEquivalent(E e, E f)`	Returns whether two elements are in the same equivalence class.
`int`	`classCount()`	Returns the number of equivalence classes in this equivalence set.
`void`	`clear()`	Removes all elements in this equivalence set.
`E`	`equiv(E e, E f)`	Marks two elements as equivalent.
`java.util.SortedMap<E,java.util.SortedSet<E>>`	`map()`	Returns a map of the canonical element in each equivalence class to the set of elements in that class.
`int`	`size()`	Returns the number of elements in this equivalence set.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - parents
```
private final java.util.Map<E extends java.lang.Comparable<E>,E extends java.lang.Comparable<E>> parents
```
- Constructor Detail
  - EquivalenceSet
```
public EquivalenceSet()
```
- Method Detail
  - add
```
public E add(E e)
```
    Adds an element, and returns the element (which is its own parent). If already present, returns the element's parent.
  - equiv
```
public E equiv(E e,
               E f)
```
    Marks two elements as equivalent. They may or may not be registered, and they may or may not be equal.
  - areEquivalent
```
public boolean areEquivalent(E e,
                             E f)
```
    Returns whether two elements are in the same equivalence class. Returns false if either or both of the elements are not registered.
  - map
```
public java.util.SortedMap<E,java.util.SortedSet<E>> map()
```
    Returns a map of the canonical element in each equivalence class to the set of elements in that class. The keys are sorted in natural order, as are the elements within each key.
  - clear
```
public void clear()
```
    Removes all elements in this equivalence set.
  - size
```
public int size()
```
    Returns the number of elements in this equivalence set.
  - classCount
```
public int classCount()
```
    Returns the number of equivalence classes in this equivalence set.