UNWIND and List Processing in Neo4j

Introduction

In Neo4j, list processing is a crucial operation, especially when working with collections of nodes and relationships. The UNWIND clause allows you to transform a list into a set of rows, enabling you to work with each item in the list individually.

What is UNWIND?

The UNWIND clause is used in Cypher to take a list and expand it into rows. Each element from the list becomes a separate row, allowing for easier manipulation and querying of data.

Basic Syntax

UNWIND  AS 
RETURN 
        

Example

WITH [1, 2, 3] AS numbers
UNWIND numbers AS num
RETURN num
        

This example takes a list of numbers and unwinds it into rows:

• 1
• 2
• 3

List Processing

In addition to UNWIND, Neo4j provides various functions to process lists, including COLLECT, FILTER, and REDUCE.

Using COLLECT

MATCH (n:Node)
RETURN COLLECT(n.property) AS properties
        

This example collects properties from nodes into a list.

Using FILTER

WITH [1, 2, 3, 4, 5] AS numbers
RETURN FILTER(num IN numbers WHERE num > 2) AS filtered
        

This example filters the list to only include numbers greater than 2.

Using REDUCE

WITH [1, 2, 3, 4] AS numbers
RETURN REDUCE(s = 0, num IN numbers | s + num) AS sum
        

This example calculates the sum of the list elements.

Best Practices

• Use UNWIND when you need to process each item in a list individually.
• Combine UNWIND with other Cypher functions for efficient data manipulation.
• Be cautious with large lists, as unwinding can lead to performance issues.

FAQ