List functions

List functions return lists of things — nodes in a path, and so on.

Further details and examples of lists may be found in Lists and List operators.

Functions:

Diagram

1. keys()

keys returns a list containing the string representations for all the property names of a node, relationship, or map.

Syntax: keys(expression)

Returns:

A list containing String elements.

Arguments:

Name Description

expression

An expression that returns a node, a relationship, or a map.

Considerations:

keys(null) returns null.

Query
MATCH (a)
WHERE a.name = 'Alice'
RETURN keys(a)

A list containing the names of all the properties on the node bound to a is returned.

Table 1. Result
keys(a)

["name","eyes","age"]

1 row

2. labels()

labels returns a list containing the string representations for all the labels of a node.

Syntax: labels(node)

Returns:

A list containing String elements.

Arguments:

Name Description

node

An expression that returns a single node.

Considerations:

labels(null) returns null.

Query
MATCH (a)
WHERE a.name = 'Alice'
RETURN labels(a)

A list containing all the labels of the node bound to a is returned.

Table 2. Result
labels(a)

["Person","Developer"]

1 row

3. nodes()

nodes() returns a list containing all the nodes in a path.

Syntax: nodes(path)

Returns:

A list containing Node elements.

Arguments:

Name Description

path

An expression that returns a path.

Considerations:

nodes(null) returns null.

Query
MATCH p =(a)-->(b)-->(c)
WHERE a.name = 'Alice' AND c.name = 'Eskil'
RETURN nodes(p)

A list containing all the nodes in the path p is returned.

Table 3. Result
nodes(p)

[Node[0]{name:"Alice",eyes:"brown",age:38},Node[1]{name:"Bob",eyes:"blue",age:25},Node[4]{array:["one","two","three"],name:"Eskil",eyes:"blue",age:41}]

1 row

4. range()

range() returns a list comprising all integer values within a range bounded by a start value start and end value end, where the difference step between any two consecutive values is constant; i.e. an arithmetic progression. To create ranges with decreasing integer values, use a negative value step. The range is inclusive for non-empty ranges, and the arithmetic progression will therefore always contain start and — depending on the values of start, step and end — end. The only exception where the range does not contain start are empty ranges. An empty range will be returned if the value step is negative and start - end is positive, or vice versa, e.g. range(0, 5, -1).

Syntax: range(start, end [, step])

Returns:

A list of Integer elements.

Arguments:

Name Description

start

An expression that returns an integer value.

end

An expression that returns an integer value.

step

A numeric expression defining the difference between any two consecutive values, with a default of 1.

Query
RETURN range(0, 10), range(2, 18, 3), range(0, 5, -1)

Three lists of numbers in the given ranges are returned.

Table 4. Result
range(0, 10) range(2, 18, 3) range(0, 5, -1)

[0,1,2,3,4,5,6,7,8,9,10]

[2,5,8,11,14,17]

[]

1 row

5. reduce()

reduce() returns the value resulting from the application of an expression on each successive element in a list in conjunction with the result of the computation thus far. This function will iterate through each element e in the given list, run the expression on e — taking into account the current partial result — and store the new partial result in the accumulator. This function is analogous to the fold or reduce method in functional languages such as Lisp and Scala.

Syntax: reduce(accumulator = initial, variable IN list | expression)

Returns:

The type of the value returned depends on the arguments provided, along with the semantics of expression.

Arguments:

Name Description

accumulator

A variable that will hold the result and the partial results as the list is iterated.

initial

An expression that runs once to give a starting value to the accumulator.

list

An expression that returns a list.

variable

The closure will have a variable introduced in its context. We decide here which variable to use.

expression

This expression will run once per value in the list, and produce the result value.

Query
MATCH p =(a)-->(b)-->(c)
WHERE a.name = 'Alice' AND b.name = 'Bob' AND c.name = 'Daniel'
RETURN reduce(totalAge = 0, n IN nodes(p)| totalAge + n.age) AS reduction

The age property of all nodes in the path are summed and returned as a single value.

Table 5. Result
reduction

117

1 row

6. relationships()

relationships() returns a list containing all the relationships in a path.

Syntax: relationships(path)

Returns:

A list containing Relationship elements.

Arguments:

Name Description

path

An expression that returns a path.

Considerations:

relationships(null) returns null.

Query
MATCH p =(a)-->(b)-->(c)
WHERE a.name = 'Alice' AND c.name = 'Eskil'
RETURN relationships(p)

A list containing all the relationships in the path p is returned.

Table 6. Result
relationships(p)

[:KNOWS[0]{},:MARRIED[4]{}]

1 row

7. reverse()

reverse() returns a list in which the order of all elements in the original list have been reversed.

Syntax: reverse(original)

Returns:

A list containing homogeneous or heterogeneous elements; the types of the elements are determined by the elements within original.

Arguments:

Name Description

original

An expression that returns a list.

Considerations:

Any null element in original is preserved.

Query
WITH [4923,'abc',521, NULL , 487] AS ids
RETURN reverse(ids)
Table 7. Result
reverse(ids)

[487,<null>,521,"abc",4923]

1 row

8. tail()

tail() returns a list lresult containing all the elements, excluding the first one, from a list list.

Syntax: tail(list)

Returns:

A list containing heterogeneous elements; the types of the elements are determined by the elements in list.

Arguments:

Name Description

list

An expression that returns a list.

Query
MATCH (a)
WHERE a.name = 'Eskil'
RETURN a.array, tail(a.array)

The property named array and a list comprising all but the first element of the array property are returned.

Table 8. Result
a.array tail(a.array)

["one","two","three"]

["two","three"]

1 row