K-Hop query is to find the neighbor nodes that a node can reach in K hops/steps the shortest, and return the list of the neighbors.

In the field of graph, the concept of K-Hop query is easily misunderstood. Ultipa defines K-Hop query as follows:

• K represents the number of steps from the start node, with a minimum value of 1;
• K-Hop neighbors are the nodes that can be reached from the start node at step K through the shortest path (set the weight of edges to 1);
• K-Hop neighbors will not appear in the neighbors of other steps, for instance, the nodes of 2-hop neighbor do not appear in the set of neighbor nodes of the 3-hop or other hops;
• The number of K-Hop neighbors refers to the number of all neighbors at step K (after deduplication).
• In finite graph, when the value of K is big enough, the number of K-Hop neighbors must be 0. Let's say a graph with diameter of 5, the 6-Hop neighbors of all nodes must all be 0.

K-Hop query is executed in a BFS (Breadth First Search) fashion to guarantee the paths to reach the neighbors are the shortest. K-Hop is a graph neighbor query function with an optimized and greatly improved performance, it is suggested to use K-Hop instead of other path query methods when querying neighbor nodes.

Syntax:

• Command: khop()
• Parameter: (see the table below)
• Statement Alias: Custom alias supported, structure type is NODE

N Hops

Example: find 10 Card CA001's 3-Hop neighbors, return all node properties

khop().src({_id == "CA001"}).depth(3) as n
limit 10 
return n{*}

1~N Hops

Example: find 10 Card CA001's neighbors within 3 hops, return all node properties

khop().src({_id == "CA001"}).depth(:3) as n
limit 10 
return n{*}

M~N Hops

Example: find 10 Card CA001's neighbors within 2~3 hops, return all node properties

khop().src({_id == "CA001"}).depth(2:3) as n
limit 10 
return n{*}

node_filter()

Example: find 10 Card CA001's neighbors within 3 hops, return all non-@card node properties

khop().src({_id == "CA001"}).depth(:3)
  .node_filter({!@card}) as n
limit 10 
return n{*}

edge_filter()

Example: find 10 Card CA001's neighbors within 3 hops, return all non-@transfer edge properties

khop().src({_id == "CA001"}).depth(:3)
  .edge_filter({!@transfer}) as n
limit 10 
return n{*}

direction(right)

Example: find Card CA001's neighbors within 3 hops, return 10 nodes that are connected by edges in the right direction (outbound) and their properties

khop().src({_id == "CA001"}).depth(:3)
  .direction(right) as n
limit 10 
return n{*}

direction(left)

Example: find Card CA001's neighbors within 3 hops, return 10 nodes that are connected by edges in the left direction (inbound) and their properties

khop().src({_id == "CA001"}).depth(:3)
  .direction(left) as n
limit 10 
return n{*}

limit

Example: find Card CA001 and Card CA002's neighbors within 3 hops, return 3 neighbors' properties for each node

uncollect ["CA001","CA002"] as n1
khop().src({_id == n1}).depth(3)
  .limit(3) as n2
return n2{*}