urns
-------
results : set or ndarray
    Set of pairs ``(i,j)``, with ``i < j``, for which the corresponding
    positions are close. If output_type is 'ndarray', an ndarry is
    returned instead of a set.

Examples
--------
You can search all pairs of points in a kd-tree within a distance:

>>> import matplotlib.pyplot as plt
>>> import numpy as np
>>> from scipy.spatial import KDTree
>>> rng = np.random.default_rng()
>>> points = rng.random((20, 2))
>>> plt.figure(figsize=(6, 6))
>>> plt.plot(points[:, 0], points[:, 1], "xk", markersize=14)
>>> kd_tree = KDTree(points)
>>> pairs = kd_tree.query_pairs(r=0.2)
>>> for (i, j) in pairs:
...     plt.plot([points[i, 0], points[j, 0]],
...             [points[i, 1], points[j, 1]], "-r")
>>> plt.show()

)