Tail Step

The tail step navigates from edges to their source (origin) vertices, allowing traversal back to where the edges start from. It transforms a stream of edges into a stream of vertices.

In this diagram:

An Input Stream contains edge elements (e.g., A->B, C->D).
The .tail() step processes each edge.
The Output Stream contains the corresponding source (tail) vertices (A, C) for each input edge.

Syntax

walker.tail()

Parameters

This step takes no parameters.

Return Value

Returns a new walker positioned at the source vertices of the edges in the current traversal.

Examples

Basic Tail Step

Find people who created projects by getting back to the source vertex:

    // Find projects created by people
    // 1. Start with all people
    // 2. Find "created" edges they made
    // 3. Use head() to get to the projects (the target vertices)
    let projects = graph
        .walk()
        .vertices(Vertex::person())
        .edges(Edge::created().outgoing())
        .head() // Move to the target vertex of the edge
        .collect::<Vec<_>>();

    println!("Found {} projects created by people", projects.len());

Multi-Step Traversal

Traverse multiple relationships to find indirect connections:

    // Find people who follow someone who created a project
    // This demonstrates chaining head and tail multiple times
    let indirect_creators = graph
        .walk()
        .vertices(Vertex::person())
        .edges(Edge::follows().outgoing())
        .tail() // Move to the people they follow
        .edges(Edge::created().outgoing())
        .tail() // Move to the projects created by those people
        .collect::<Vec<_>>();

    println!(
        "Found {} projects created by people the original people know",
        indirect_creators.len()
    );

Best Practices

Always follow edge traversals with either head() or tail() to return to vertices.
Use contexts to retain information about the edge when moving back to the source vertex via tail().
Remember that tail() returns the source vertex (where the edge starts).
For retrieving both endpoints, consider using context to store one while visiting the other.

Common Use Cases

Author identification: Finding who created something by looking at edge sources (tail()).
Relationship sources: Identifying the initiators of connections (tail()).
Backtracking: Returning to source vertices after examining edges (tail()).
Edge-based filtering: Finding vertices that have specific incoming edges (by traversing the edge and using tail()).

graph-api