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## 7.12. Calculating the clustering coefficient of a network

Graph

In this example, adapted from Niko Gamulins blog post on Neo4j for Social Network Analysis, the graph in question is showing the 2-hop relationships of a sample person as nodes with `KNOWS` relationships.

The clustering coefficient of a selected node is defined as the probability that two randomly selected neighbors are connected to each other. With the number of neighbors as `n` and the number of mutual connections between the neighbors `r` the calculation is:

The number of possible connections between two neighbors is `n!/(2!(n-2)!) = 4!/(2!(4-2)!) = 24/4 = 6`, where `n` is the number of neighbors `n = 4` and the actual number `r` of connections is `1`. Therefore the clustering coefficient of node 1 is `1/6`.

`n` and `r` are quite simple to retrieve via the following query:

Query

    START a = node(1)
    MATCH (a)--(b)
    WITH a, count(distinct b) as n
    MATCH (a)--()-[r]-()--(a)
    RETURN n, count(distinct r) as r

This returns `n` and `r` for the above calculations.

Result

n | r
--- | ---
1 row
0 ms
`4` | `1`

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