nearest_neighbor.pas

var
    x : array[0..99] of single;
    y : array[0..99] of single;
    i : Integer;
    N : Integer;
    s : Integer;
    nn : Integer;
    x_s : single;
    y_s : single;
    x_dist : single;
    y_dist : single;
    dist : single;
    nearest_dist : single;
    nearest_idx : Integer;

begin
    N := 100;
    // initialize coordinates
    for i := 1 to N do
    begin
        x[i] := Random;
        y[i] := Random;
    end;

    // find nearest neighbor of one
    s := Random(N);
    x_s := x[s];
    y_s := y[s];
    nearest_dist := 10;
    for i := 1 to N do
    begin
        if i <> s then
        begin
            x_dist := x_s - x[i];
            y_dist := y_s - y[i];
            dist := Sqrt(x_dist*x_dist + y_dist*y_dist);
            if nearest_dist > dist then
            begin
                nearest_dist := dist;
                nearest_idx := i;
            end;
        end;
    end;
end.

nearest_neighbor.py

#!/usr/bin/env python

import numpy as np
import scipy.spatial as sp


def main():
    N = 10
    x = np.random.random((N, 2))
    tree = sp.cKDTree(x)
    for i in range(N):
        dist, idx = tree.query(x[i], k=2, distance_upper_bound=4)
        print(dist[-1], idx[-1])


if __name__ == '__main__':
    main()

0.165303482593 6                 
0.232515858306 4                 
0.218432027652 9                 
0.17886330167 8                  
0.171672012593 0                 
0.451214834747 2                 
0.165303482593 0                 
0.316582339776 6                 
0.17886330167 3                  
0.218432027652 2