org.apache.arrow.algorithm.dictionary

Class SearchTreeBasedDictionaryBuilder<V extends ValueVector>

java.lang.Object

org.apache.arrow.algorithm.dictionary.SearchTreeBasedDictionaryBuilder<V>

Type Parameters:

V - the dictionary vector type.

public class SearchTreeBasedDictionaryBuilder<V extends ValueVector>
extends Object

A dictionary builder is intended for the scenario frequently encountered in practice: the dictionary is not known a priori, so it is generated dynamically. In particular, when a new value arrives, it is tested to check if it is already in the dictionary. If so, it is simply neglected, otherwise, it is added to the dictionary.

This class builds the dictionary based on a binary search tree. Each add operation can be finished in O(log(n)) time, where n is the current dictionary size.

The dictionary builder is intended to build a single dictionary. So it cannot be used for different dictionaries.

Below gives the sample code for using the dictionary builder

 SearchTreeBasedDictionaryBuilder dictionaryBuilder = ...
 ...
 dictionaryBuild.addValue(newValue);
 ...
 

With the above code, the dictionary vector will be populated, and it can be retrieved by the getDictionary() method. After that, dictionary encoding can proceed with the populated dictionary.

Field Summary

Fields

Modifier and Type	Field and Description
protected VectorValueComparator<V>	comparator The criteria for sorting in the search tree.

Constructor Summary

Constructors

Constructor and Description
SearchTreeBasedDictionaryBuilder(V dictionary, VectorValueComparator<V> comparator) Construct a search tree-based dictionary builder.
SearchTreeBasedDictionaryBuilder(V dictionary, VectorValueComparator<V> comparator, boolean encodeNull) Construct a search tree-based dictionary builder.

Method Summary

Modifier and Type	Method and Description
int	addValue(V targetVector, int targetIndex) Try to add an element from the target vector to the dictionary.
int	addValues(V targetVector) Try to add all values from the target vector to the dictionary.
V	getDictionary() Gets the dictionary built.
void	populateSortedDictionary(V sortedDictionary) Gets the sorted dictionary.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

comparator

protected final VectorValueComparator<V extends ValueVector> comparator

The criteria for sorting in the search tree.

Constructor Detail

SearchTreeBasedDictionaryBuilder

public SearchTreeBasedDictionaryBuilder(V dictionary,
                                        VectorValueComparator<V> comparator)

Construct a search tree-based dictionary builder.

Parameters:

dictionary - the dictionary vector.

comparator - the criteria for value equality.

SearchTreeBasedDictionaryBuilder

public SearchTreeBasedDictionaryBuilder(V dictionary,
                                        VectorValueComparator<V> comparator,
                                        boolean encodeNull)

Construct a search tree-based dictionary builder.

Parameters:

dictionary - the dictionary vector.

comparator - the criteria for value equality.

encodeNull - if null values should be added to the dictionary.

Method Detail

getDictionary

public V getDictionary()

Gets the dictionary built. Please note that the dictionary is not in sorted order. Instead, its order is determined by the order of element insertion. To get the dictionary in sorted order, please use populateSortedDictionary(ValueVector).

Returns:

the dictionary.

addValues

public int addValues(V targetVector)

Try to add all values from the target vector to the dictionary.

Parameters:

targetVector - the target vector containing values to probe.

Returns:

the number of values actually added to the dictionary.

addValue

public int addValue(V targetVector,
                    int targetIndex)

Try to add an element from the target vector to the dictionary.

Parameters:

targetVector - the target vector containing new element.

targetIndex - the index of the new element in the target vector.

Returns:

the index of the new element in the dictionary.

populateSortedDictionary

public void populateSortedDictionary(V sortedDictionary)

Gets the sorted dictionary. Note that given the binary search tree, the sort can finish in O(n).