Package org.apache.druid.query.rowsandcols

Class RearrangedRowsAndColumns

java.lang.Object

org.apache.druid.query.rowsandcols.RearrangedRowsAndColumns

All Implemented Interfaces:

RowsAndColumns

public class RearrangedRowsAndColumns
extends Object
implements RowsAndColumns

This class exists to "decorate" a rows and columns such that it pretends to exist in a new ordering.

The constructor generally takes an int[] of pointers, these pointers are used to re-map the rows from the RowsAndColumns object. That is, if the RowsAndColumns has 4 rows and the array new int[]{3, 1, 2, 0} is passed in, then the order of traverals of the rows will be 3 -> 1 -> 2 -> 0.

This can be useful for sorting potentially immutable data, as the list of pointers can identify the order that the rows should be traversed in. It can also be used for clustering like-data together.

While this avoids a copy, in cases where the data will be iterated regularly, it also generates a random-access pattern that is not always optimal.

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.druid.query.rowsandcols.RowsAndColumns

RowsAndColumns.RowsAndColumnsDeserializer, RowsAndColumns.RowsAndColumnsSerializer

Constructor Summary

Constructors

Constructor	Description
RearrangedRowsAndColumns(int[] pointers, int start, int end, RowsAndColumns rac)
RearrangedRowsAndColumns(int[] pointers, RowsAndColumns rac)

Method Summary

Modifier and Type	Method	Description
Column	findColumn(String name)	Finds a column by name.
Collection<String>	getColumnNames()	The set of column names available from the RowsAndColumns
int	numRows()	The number of rows in the RowsAndColumns object

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.druid.query.rowsandcols.RowsAndColumns

as

Constructor Details

RearrangedRowsAndColumns

public RearrangedRowsAndColumns(int[] pointers,
 RowsAndColumns rac)

RearrangedRowsAndColumns

public RearrangedRowsAndColumns(int[] pointers,
 int start,
 int end,
 RowsAndColumns rac)

Method Details

getColumnNames

public Collection<String> getColumnNames()

Description copied from interface: RowsAndColumns

The set of column names available from the RowsAndColumns

Specified by:

getColumnNames in interface RowsAndColumns

Returns:

The set of column names available from the RowsAndColumns

numRows

public int numRows()

Description copied from interface: RowsAndColumns

The number of rows in the RowsAndColumns object

Specified by:

numRows in interface RowsAndColumns

Returns:

the integer number of rows

findColumn

@Nullable
public Column findColumn(String name)

Description copied from interface: RowsAndColumns

Finds a column by name. null is returned if the column is not found. The RowsAndColumns object should not attempt to default not-found columns to pretend as if they exist, instead the user of the RowsAndColumns object should decide the correct semantic interpretation of a column that does not exist. It is expected that most locations will choose to believe that the column does exist and is always null, but there are often optimizations that can effect this same assumption without doing a lot of extra work if the calling code knows that it does not exist.

Specified by:

findColumn in interface RowsAndColumns

Parameters:

name - the name of the column to find

Returns:

the Column, if found. null if not found.