io.lettuce.core.search.aggregateutils

Class Reducer<K>

java.lang.Object

io.lettuce.core.search.aggregateutils.Reducer<K>

Type Parameters:

K - Key type.

Direct Known Subclasses:

Reducers.Avg, Reducers.Count, Reducers.CountDistinct, Reducers.CountDistinctish, Reducers.FirstValue, Reducers.Max, Reducers.Min, Reducers.Quantile, Reducers.RandomSample, Reducers.Stddev, Reducers.Sum, Reducers.ToList

@Experimental
public abstract class Reducer<K>
extends Object

Abstract reducer for GROUPBY operations in FT.HYBRID and FT.AGGREGATE commands. Instances are created via Reducers.

Reducers handle group entries in a GROUPBY operation, performing aggregate operations like counting, summing, averaging, or finding min/max values. Each reducer can have an optional alias using the AS keyword.

Example Usage:

 
 // Count items in each group
 Reducers.count().as("item_count")

 // Sum numeric values
 Reducers.sum("@sales").as("total_sales")

 // Calculate average
 Reducers.avg("@price").as("average_price")

 // Quantile with percentile parameter
 Reducers.quantile("@price", 0.5).as("median_price")

 // First value with optional sort by
 Reducers.firstValue("@name").by("@timestamp").as("first_name")

 // Random sample
 Reducers.randomSample("@id", 10).as("sample_ids")
 
 

Since:

7.5

Author:

Aleksandar Todorov

See Also:

Reducers, ReduceFunction, GroupBy, FT.AGGREGATE, FT.HYBRID

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Reducer(ReduceFunction function) Creates a new reducer with the specified function.
protected	Reducer(String function) Creates a new reducer with the specified function name.

Method Summary

Modifier and Type	Method and Description
<T extends Reducer<K>> T	as(K alias) Set an alias for the reducer result using AS keyword.
<V> void	build(CommandArgs<K,V> args) Build the reducer into command args.
String	getFunction() Get the reduce function name.
protected abstract List<Object>	getOwnArgs() Get the reducer-specific arguments.

Methods inherited from class java.lang.Object

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

Constructor Detail

Reducer

protected Reducer(ReduceFunction function)

Creates a new reducer with the specified function.

Parameters:

function - the reduce function enum

Reducer

protected Reducer(String function)

Creates a new reducer with the specified function name. Use this constructor for custom or future reduce functions not yet defined in ReduceFunction.

Parameters:

function - the reduce function name (e.g., "COUNT", "SUM", "MY_CUSTOM_REDUCER")

Method Detail

getFunction

public final String getFunction()

Get the reduce function name.

Returns:

the reduce function name

getOwnArgs

protected abstract List<Object> getOwnArgs()

Get the reducer-specific arguments.

Returns:

list of reducer-specific arguments

as

public <T extends Reducer<K>> T as(K alias)

Set an alias for the reducer result using AS keyword.

Parameters:

alias - the alias name

Returns:

this reducer

build

public final <V> void build(CommandArgs<K,V> args)

Build the reducer into command args.

Format: REDUCE function nargs arg [arg ...] [AS name]

Type Parameters:

V - value type

Parameters:

args - the command args to build into