How can I use neo4j cypher query to create a histogram of nodes bucketed by number of relationships?

Question

I have a big bunch of nodes which match the following cypher:

(:Word)<-[:Searched]-(:Session)

I want to make a histogram of the number of Word nodes at each frequency of Searched relationships.

I want to make this sort of chart:

Searches Words
0        100
1-5      200
6-10     150
11-15    50
16-20    25

I'm just starting out with neo4j, and I'm not sure how to approach this or even if there is a way to specify this in cypher. The closest I've got is to count the relationships and get averages.

MATCH (n:Word) 
RETURN
DISTINCT labels(n),
count(*) AS NumofNodes,
avg(size((n)<-[:Searched]-())) AS AvgNumOfRelationships,
min(size((n)<-[:Searched]-())) AS MinNumOfRelationships,
max(size((n)<-[:Searched]-())) AS MaxNumOfRelationships

That is based on an example here: https://neo4j.com/developer/kb/how-do-i-produce-an-inventory-of-statistics-on-nodes-relationships-properties/

I've also seen use of the modulus operator for grouping to get buckets, though I'm not sure how to use that in reference to the count: Neo4j cypher time interval histogram query of time tree

Is there a "best" way to do this?

Answer 1

The following should work:

WITH 5 AS gSize
MATCH (w:Word)
OPTIONAL MATCH (w)<-[s:Searched]-()
WITH gSize, w, TOINT((COUNT(s) + (gSize-1))/gSize * gSize) AS m
RETURN
  CASE m WHEN 0 THEN '0' ELSE (m-gSize+1)+'-'+m END AS range,
  COUNT(*) AS ct
ORDER BY range;

With the sample data provided by @GaborSzarnyas, the output is:

+-------------+
| range  | ct |
+-------------+
| "0"    | 1  |
| "1-5"  | 1  |
| "6-10" | 1  |
+-------------+

Answer 2

I was able to figure out a query which I think gets me the data I want:

MATCH (n:Word) 
WITH n, 5 AS bucketsize
WITH (FLOOR(SIZE( (n)<-[:Searched]-() ) / bucketsize) * bucketsize) AS numRels
RETURN numRels, COUNT(*)
ORDER BY numRels ASC

It doesn't get the zero row, which I'd like to have, but it seems like it works otherwise. Hopefully someone else has a better solution.

Answer 3

I created a simple example dataset of three words: w1 with no searches, w2 with 3 searches and w3 with 6.

CREATE (w1:Word {w: '1'})
WITH count(*) AS dummy

CREATE (w2:Word {w: '2'}) WITH w2
UNWIND range(1, 3) AS i
CREATE (w2)<-[:Searched]-(:Session)
WITH count(*) AS dummy

CREATE (w3:Word {w: '3'}) WITH w3
UNWIND range(1, 6) AS i
CREATE (w3)<-[:Searched]-(:Session)

I would approach it like this: first, let's create a list with the upper limits for each bucket:

RETURN [i IN range(0, 4) | i*5] AS upperLimits

╒══════════════╕
│"upperLimits" │
╞══════════════╡
│[0,5,10,15,20]│
└──────────────┘

Second, use this with a list comprehension that selects the elements from the list that has a sufficiently large upper limit. The first one of these is our bucket, so we select that with the [0] list indexer. The rest is just calculating the lower limit and ordering rows:

WITH [i IN range(0, 4) | i*5] AS upperLimits
MATCH (n:Word) 
WITH upperLimits, ID(n) AS n, size((n)<-[:Searched]-()) AS numOfRelationships
WITH
  [upperLimit IN upperLimits WHERE numOfRelationships <= upperLimit][0] AS upperLimit,
  count(n) AS count
RETURN
  upperLimit - 4 AS lowerLimit,
  upperLimit,
  count
ORDER BY lowerLimit

The query gives the following results:

╒════════════╤════════════╤═══════╕
│"lowerLimit"│"upperLimit"│"count"│
╞════════════╪════════════╪═══════╡
│-4          │0           │1      │
├────────────┼────────────┼───────┤
│1           │5           │1      │
├────────────┼────────────┼───────┤
│6           │10          │1      │
└────────────┴────────────┴───────┘

Potential improvements:

(1) If the value of numOfRelationships is larger than the largest upper limit, the query above will return the first element of an empty list, which is null . To avoid that, either 1) set a sufficiently large upper limit, eg

MATCH (n:Word) 
WITH max(size((n)<-[:Searched]-())) AS maxNumberOfRelationShips
WITH [i IN range(-1, maxNumberOfRelationShips/5+1) | {lower: i*5-4, upper: i*5}] AS limits
RETURN *

You can use the top bucket with "16 or larger" semantics with coalesce .

(2) -4 as a lower limit is not very nice, we can use CASE to get rid of it.

Putting all this together, we get this:

MATCH (n:Word) 
WITH max(size((n)<-[:Searched]-())) AS maxNumberOfRelationShips
WITH [i IN range(0, maxNumberOfRelationShips/5+1) | i*5] AS upperLimits
MATCH (n:Word) 
WITH upperLimits, ID(n) AS n, size((n)<-[:Searched]-()) AS numOfRelationships
WITH
  [upperLimit IN upperLimits WHERE numOfRelationships <= upperLimit][0] AS upperLimit,
  count(n) AS count
RETURN 
  CASE WHEN upperLimit - 4 < 0 THEN 0 ELSE upperLimit - 4 END AS lowerLimit,
  upperLimit,
  count
ORDER BY lowerLimit

Which results in:

╒════════════╤════════════╤═══════╕
│"lowerLimit"│"upperLimit"│"count"│
╞════════════╪════════════╪═══════╡
│0           │0           │1      │
├────────────┼────────────┼───────┤
│1           │5           │1      │
├────────────┼────────────┼───────┤
│6           │10          │1      │
└────────────┴────────────┴───────┘

Answer 4

What I usually do in this scenario is that I use the setting in neo4j that if you divide an integer by an integer you get back an integer. This simplifies the query alot. We add a special case for 0 and it all fits in one line.

WITH [0,1,5,7,9,11] as list
UNWIND list as x
WITH CASE WHEN x = 0 THEN -1 ELSE  (x / 5) * 5 END as results
return results

This returns

-1, 0, 5, 5, 5, 10

Which is not ideal given that you want to group 1-5 together but good enough i guess.