Find the nearest point in distance for all the points in the dataset - Python

Question

I have a dataset as follows,

Id     Latitude      longitude
1      25.42         55.47
2      25.39         55.47
3      24.48         54.38
4      24.51             


        

Answer 1

You can do this very efficiently by calling a library that implements smart algorithms for this, one example would be sklearn which has a NearestNeighbors method that does exactly this.

Example of the code modified to do this:

from sklearn.neighbors import NearestNeighbors
import numpy as np

def distance(p1, p2):
    """
    Calculate the great circle distance between two points
    on the earth (specified in decimal degrees)
    """
    lon1, lat1 = p1
    lon2, lat2 = p2
    # convert decimal degrees to radians
    lon1, lat1, lon2, lat2 = map(np.radians, [lon1, lat1, lon2, lat2])
    # haversine formula
    dlon = lon2 - lon1
    dlat = lat2 - lat1
    a = np.sin(dlat/2)**2 + np.cos(lat1) * np.cos(lat2) * np.sin(dlon/2)**2
    c = 2 * np.arcsin(np.sqrt(a))
    km = 6367 * c
    return km

points = [[25.42, 55.47],
          [25.39, 55.47],
          [24.48, 54.38],
          [24.51, 54.54]]

nbrs = NearestNeighbors(n_neighbors=2, metric=distance).fit(points)

distances, indices = nbrs.kneighbors(points)

result = distances[:, 1]

which gives

>>> result
array([  1.889697  ,   1.889697  ,  17.88530556,  17.88530556])