FOR

Overview

The FOR statement unnests a list into individual records and expands the intermediate result table accordingly.

Syntax
<for statement> ::= 
  "FOR" <binding variable> "IN" <list value expression> [ <ordinality or offset> ]

<ordinality or offset> ::= 
  "WITH" { "ORDINALITY" | "OFFSET" } <binding variable>

Details

• The <ordinality or offset> defines a variable to track the position of elements in the list:
  • ORDINALITY provides the ordinal position of each element, i.e., 1, 2, 3,....
  • OFFSET provides the zero-based position of each element, i.e., 0, 1, 2, ...
• The name of the <binding variable> in <ordinality or offset> must differ from the <binding variable> placed right after FOR.

Unnesting a Simple List

GQL
FOR item IN [1,1,2,3,null]
RETURN item

Result:

GQL
FOR item IN [[1,2], [2,3,5]]
RETURN item

Result:

Unnesting a Variable

GQL
LET user = "Alex"
LET interests = ["tennis", "violin"]
FOR interest IN interests
RETURN user, interest

Result:

In this query, the FOR statement unnests the list contained in the interests column of the working table into two records. Consequently, the corresponding record in the user column is duplicated to two records as well.

Unnesting a Group Variable

GQL
INSERT (c1:Card {_id: 'C1'}),
  	   (c2:Card {_id: 'C2'}),
  	   (c3:Card {_id: 'C3'}),
  	   (c4:Card {_id: 'C4'}),
  	   (c5:Card {_id: 'C5'}),
       (c1)-[:Transfers {label: 'normal'}]->(c2),
       (c1)-[:Transfers {label: 'abnormal'}]->(c5),
       (c5)-[:Transfers {label: 'normal'}]->(c2),
       (c5)-[:Transfers {label: 'abnormal'}]->(c4),
       (c2)-[:Transfers {label: 'normal'}]->(c3),
       (c4)-[:Transfers {label: 'normal'}]->(c3)

Retrieve one shortest path between C1 and C3, and return the label values on edges in the path:

GQL
MATCH SHORTEST 1 ({_id: "C1"})-[trans:Transfers]-{1,6}({_id: "C3"})
FOR tran IN trans
RETURN tran.label

Result:

In this query, the trans declared in a quantified path is a group variable. To convert it to a singleton degree of reference, you can use FOR to unnest it.

WITH ORDINALITY

To collect elements in even positions from a list to a new list:

GQL
FOR item in ["a", "b", "c", "d"] WITH ORDINALITY index // index starts from 1
FILTER index %2 = 0
RETURN collect_list(item)

Result:

WITH OFFSET

Return the second element in a list:

GQL
FOR item in ["a", "b", "c", "d"] WITH OFFSET index // index starts from 0
FILTER index = 1
RETURN item

Result: