Function nearest_neighbor_graph 

pub fn nearest_neighbor_graph(
    points: &[Vec<f64>],
    metric: DistanceMetric,
    k: i64,
    cutoff: f64,
    directed: bool,
) -> IgraphResult<Graph>

Build the k-nearest-neighbor graph of a point set.

points holds one row per point with a shared, arbitrary dimensionality (inferred from the first row). For each point the k nearest other points within cutoff are connected by an outgoing arc.

• metric — DistanceMetric::Euclidean (L2) or DistanceMetric::Manhattan (L1).
• k — maximum neighbours per point; a negative value means “no limit” (every point within cutoff). k == 0 produces an edgeless graph.
• cutoff — maximum connection distance; a negative value (or f64::INFINITY) means “no cutoff”. The comparison is strict, so a point exactly at distance cutoff is excluded.
• directed — when false, the directed neighbour graph is collapsed to undirected, merging reciprocal arcs into one edge.

Errors

• IgraphError::InvalidArgument if the points are zero-dimensional (and there is at least one point).
• IgraphError::InvalidArgument if the rows have inconsistent dimensionality.

Examples

use rust_igraph::{nearest_neighbor_graph, DistanceMetric};

// Three points on a line: each links to its single nearest neighbour.
let pts = vec![vec![0.0], vec![1.0], vec![5.0]];
let g = nearest_neighbor_graph(&pts, DistanceMetric::Euclidean, 1, -1.0, true).unwrap();
assert!(g.is_directed());
assert_eq!(g.vcount(), 3);
// 0→1, 1→0, 2→1
assert_eq!(g.ecount(), 3);