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()).