Testing elements of a list
Cypher has a number of list predicate functions that help you to test if:

all elements satisfy the criteria.

one or more elements satisfy the criteria.

a list is empty.

no elements in a list satisfy the criteria.

at most a single element satisfies the criteria.
all()
You can all() to return true if all elements in a list satisfy the criteria.
Here is an example:
MATCH p = (a:Actor)[:ACTED_IN*2](a2:Actor)
WHERE
a.name = 'Meg Ryan'
AND all(x IN nodes(p) WHERE x.year > 1900 OR x:Actor)
RETURN p
The test here for the list of nodes in the path is whether the year property is greater than 1900 (for a movie node) or whether the node type is an Actor. If this test evaluates to true, then the path is returned.
Here is an example where all()
returns false:
MATCH p = (a:Actor)[:ACTED_IN*2](a2:Actor)
WHERE
a.name = 'Meg Ryan'
AND all(x IN nodes(p) WHERE x.year > 2010 OR x:Actor)
RETURN p
Not every node in the list has a value of 2010 for the year property or is an Actor. Because not all elements in the list pass the criteria, all()
returns false.
For this query no paths are returned.
This query will also have all()
evaluate to false because the list of nodes contains both Actor nodes and Movie nodes, and it cannot return all elements of the list:
MATCH p = (a:Actor)[:ACTED_IN*2](a2:Actor)
WHERE
a.name = 'Meg Ryan'
AND all(x IN nodes(p) WHERE x.year > 1900)
RETURN p
any()
This function returns true if one or more elements in the list satisfy the criteria:
MATCH p = (a:Actor)[:ACTED_IN*2](a2:Actor)
WHERE
a.name = 'Meg Ryan'
AND any(x IN nodes(p) WHERE x.year = 2000)
RETURN p
This query returns the paths from Meg Ryan to other actors for movies released in the year 2000. In this case there are two movies.
isEmpty()
This function returns true if the list is empty.
MATCH (m:Movie)
WITH collect(m.title) AS Movies
RETURN isEmpty(Movies)
Which performs the same as:
MATCH (m:Movie)
WITH collect(m.title) AS Movies
RETURN size(Movies) = 0
none()
This function returns true if none of the elements satisfy the criteria. Here is an example:
MATCH p = (a:Actor)[:ACTED_IN*2](a2:Actor)
WHERE
a.name = 'Meg Ryan'
AND none(x IN nodes(p) WHERE x.name= 'Tom Hanks' and x:Actor)
RETURN p
This query will return all paths that do not include both Meg Ryan and Tom Hanks.
We test whether Tom Hanks is in the path and if he is not, then the path is returned.
If you were to run this query where you comment out the AND
clause, you will see that more paths are returned.
single()
This function returns true if only one of the elements satisfy the criteria. Here is an example:
MATCH p = (a:Actor)[:ACTED_IN*2](a2:Actor)
WHERE
a.name = 'Tom Hanks'
AND single(x IN nodes(p) WHERE x.born.year = a.born.year AND x:Actor)
RETURN a.born.year, a2.born.year, a2.name
Each path’s nodes are tested to see if there is more than one Actor node that has the same value as the year of birth of Tom Hanks. If the path has more than one node with the same birth year, it returns false.
If you were you comment out the AND
clause, you would see that the query returns more rows.
For example the actor Kim Cattrall was born in the same year as Tom Hanks and is excluded from the result.
Check your understanding
1. At least one element in a list
Suppose you want to test whether at least one element with a given value is in a list. What predicate function do you use?

❏
some()

✓
any()

❏
oneOrMore()
Hint
You want to return true if any element in the list satisfies the criteria.
Solution
You use the any()
function to return true if any element in the list satisfies the criteria.
2. Year 2000 Movies for Meg Ryan
We want to know the paths from Meg Ryan to other actors for movies that were released in 2000. How do you test this for the paths from Meg Ryan to other actors?
Use the dropdown below to select the correct code.
Once you have selected your option, click the Check Results query button to continue.
MATCH p = (a:Actor)[:ACTED_IN*2](a2:Actor)
WHERE
a.name = 'Meg Ryan'
/*select:AND all(x IN nodes(p) WHERE x.year = 2000 OR x:Actor)*/
RETURN p

❏
AND none(x IN nodes(p) WHERE x.year = 2000 OR x:Actor)

✓
AND all(x IN nodes(p) WHERE x.year = 2000 OR x:Actor)

❏
AND any(x IN nodes(p) WHERE x.year = 2000 OR x:Actor)

❏
AND some(x IN nodes(p) WHERE x.year = 2000 OR x:Actor)
Hint
You want to test if all nodes in the path are either a movie released in 2000 or is a node with the Actor label.
Solution
The correct answer is AND all(x IN nodes(p) WHERE x.year = 2000 OR x:Actor)
Summary
In this lesson, you learned how to use Cypher predicate functions. In the next Challenge, you will create a query that uses a predicate function.