Step - flatMap

flatMap(traversal) (also flat_map) replaces each traverser by every result of a child traversal run on it (TinkerPop FlatMapStep). A traverser for which the child yields nothing is dropped.

g.V("1").flatMap(__.out().values("name")).to_list()    // ["josh", "lop", "vadas"]
g.V().flatMap(__.out().out()).path().by("name").to_list()
// [["marko", "ripple"], ["marko", "lop"]]
g.V().local(__.out().out()).path().by("name").to_list()
// [["marko", "josh", "ripple"], ["marko", "josh", "lop"]]

The last two queries show the difference to local(): flatMap() hides the child's steps from path() (each result is one new position after the incoming path), while local() continues the child's own path.

• The child sees the incoming traverser with its path, sack and labels.
• Bulk is kept: the results of a merged traverser carry its bulk.

For only the first result, use map().

Rust: GraphTraversalSource::flat_map(traversal), __::flat_map(traversal).