java.lang.Object
- org.apache.druid.frame.key.ClusterBy

```
public class ClusterBy
extends Object
```
Describes a key used for sorting or partitioning. Keys have columns, and some of those columns may comprise a "bucket key". See getBucketByCount() for details about bucket keys.

Constructor Summary

Constructors
Constructor Description

ClusterBy(List<KeyColumn> columns, int bucketByCount)

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`Comparator<RowKey>`	`bucketComparator(RowSignature rowSignature)`	Comparator that compares bucket keys for this instance.
`Comparator<byte[]>`	`byteKeyComparator(RowSignature rowSignature)`	Comparator that compares byte arrays of keys for this instance using the given signature directly.
`boolean`	`equals(Object o)`
`int`	`getBucketByCount()`	How many fields from `getColumns()` comprise the "bucket key".
`List<KeyColumn>`	`getColumns()`	The columns that comprise this key, in order.
`int`	`hashCode()`
`boolean`	`isEmpty()`	Whether this key is empty.
`Comparator<RowKey>`	`keyComparator(RowSignature rowSignature)`	Comparator that compares keys for this instance using the given signature.
`RowKeyReader`	`keyReader(ColumnInspector inspector)`	Create a reader for keys for this instance.
`static ClusterBy`	`none()`	Create an empty key.
`boolean`	`sortable()`	Whether this key is sortable.
`String`	`toString()`

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

- Constructor Detail
  - ClusterBy
```
public ClusterBy(List<KeyColumn> columns,
                 int bucketByCount)
```
- Method Detail
  - none
```
public static ClusterBy none()
```
    Create an empty key.
  - getColumns
```
public List<KeyColumn> getColumns()
```
    The columns that comprise this key, in order.
  - getBucketByCount
```
public int getBucketByCount()
```
    How many fields from getColumns() comprise the "bucket key". Bucketing is like strict partitioning: all rows in a given partition will have the exact same bucket key. It is most commonly used to implement segment granularity during ingestion. The bucket key is a prefix of the complete key. Will always be less than, or equal to, the size of getColumns(). Only relevant when a ClusterBy instance is used as a partitioning key.
  - isEmpty
```
public boolean isEmpty()
```
    Whether this key is empty.
  - sortable
```
public boolean sortable()
```
    Whether this key is sortable. Empty keys (with no columns) are considered sortable.
  - keyReader
```
public RowKeyReader keyReader(ColumnInspector inspector)
```
    Create a reader for keys for this instance. The provided ColumnInspector is used to determine the types of fields in the keys. The provided signature does not have to exactly match the sortColumns: it merely has to contain them all.
  - keyComparator
```
public Comparator<RowKey> keyComparator(RowSignature rowSignature)
```
    Comparator that compares keys for this instance using the given signature.
  - byteKeyComparator
```
public Comparator<byte[]> byteKeyComparator(RowSignature rowSignature)
```
    Comparator that compares byte arrays of keys for this instance using the given signature directly.
  - bucketComparator
```
public Comparator<RowKey> bucketComparator(RowSignature rowSignature)
```
    Comparator that compares bucket keys for this instance. Bucket keys are retrieved by calling RowKeyReader.trim(RowKey, int) with getBucketByCount().
  - equals
```
public boolean equals(Object o)
```
    Overrides:
    
    equals in class Object
  - hashCode
```
public int hashCode()
```
    Overrides:
    
    hashCode in class Object
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object

Class ClusterBy

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

ClusterBy

Method Detail

none

getColumns

getBucketByCount

isEmpty

sortable

keyReader

keyComparator

byteKeyComparator

bucketComparator

equals

hashCode

toString