List Functions

Example Graph

GQL
INSERT (p1:Paper {_id:'P1', title:'Efficient Graph Search', score:6, author:'Alex'}),
       (p2:Paper {_id:'P2', title:'Optimizing Queries', score:9, author:'Alex'}),
       (p3:Paper {_id:'P3', title:'Path Patterns', score:7, author:'Zack'}),
       (p1)-[:Cites {weight:2}]->(p2),
       (p2)-[:Cites {weight:1}]->(p3)

head()

Returns the first element in a list.

GQL
LET myList = ["a", 1, 2]
RETURN head(myList)

Result: "a"

last()

Returns the last element of a list.

GQL
RETURN last([1, 2, 3])

Result: 3

tail()

Returns all elements of a list except the first.

GQL
RETURN tail([1, 2, 3, 4])

Result: [2, 3, 4]

size()

Returns the number of elements in a list.

GQL
LET myList = [1, 2, null, 3]
RETURN size(myList)

Result:

reverse()

Returns a list with elements in reversed order.

GQL
RETURN reverse([1, 2, 3])

Result: [3, 2, 1]

append()

Adds an element to the end of a list and returns the new list.

GQL
LET myList = ["a", 1, 2]
RETURN append(myList, "b")

Result: ["a",1,2,"b"]

range()

Generates a list of integers from start to end (inclusive), with an optional step.

GQL
RETURN range(1, 5), range(0, 10, 3)

Result: [1, 2, 3, 4, 5], [0, 3, 6, 9]

list_contains()

Returns true if a value exists in a specified list.

GQL
LET myList = ["a", 1, 2]
RETURN list_contains(myList, "b")

Result: false

list_union()

Returns the union of two lists, producing a new list of elements from either input list. Duplicates are removed.

GQL
LET l1 = [1,2,2,3], l2 = [3,4,5]
RETURN list_union(l1, l2)

Result: [1,2,3,4,5]

intersection()

Returns the intersection of two lists, producing a new list of elements common to both. Duplicates are removed.

GQL
LET l1 = [1,2,3,3], l2 = [3,3,4,5]
RETURN intersection(l1, l2)

Result: [3]

difference()

Returns the difference between two lists, producing a new list of elements found in the first list but not in the second. Duplicates are removed.

GQL
LET l1 = [1,2,2,3], l2 = [3,4,5]
RETURN difference(l1, l2)

Result: [1,2]

list_sort()

Sorts a list.

GQL
RETURN list_sort([3, 1, 4, 1, 5])

Result: [1, 1, 3, 4, 5]

list_filter()

Filters a list of records, nodes, or edges by checking a property against a value using an operator.

GQL
MATCH (n:Paper)
LET papers = collect_list(n)
RETURN list_filter(papers, "score", ">", 7)

Result:

JSON
[
  {"id": "P2", "labels": ["Paper"], "properties": {"title": "Optimizing Queries", "score": 9, "author": "Alex"}}
]

reduce()

Performs a calculation iteratively using each element in a list. With a specified intital value, the defined calculation takes the first element in the list as input.

GQL
LET myList = [1,3,5]
RETURN reduce(_sum = 0, item in myList | _sum + item) AS listSum

Result: 9

GQL
MATCH p = ({_id: "P1"})-[edges]->{2}()
RETURN reduce(total = 0, edge in edges | total + edge.weight)

Result: 3