在 Pandas 中查找 2 系列点之间的距离，最快迭代

Question

Have 2 sets of data, 1 which contains coordinates of fixed location called locations

And a secondary table of vehicle movements called movements

What would be the fastest way to iterate through both tables to find if any of the movements are within a certain distance of a location, eg the Euclidean distance between a point on the movements and a point on any of the locations?

Currently am using a nested loop which is incredibly slow. Both pandas df have been converted using

locations_dict=locations.to_dict('records')
movements_dict=movements.to_dict('records')

then iterated via:

for movement in movements_dict:
    visit='no visit'
    for location in locations_dict:
        distance = np.sqrt((location['Latitude']-movement['Lat'])**2+(location['Longitude']-movement['Lng'])**2)
        if distance < 0.05:
            visit=location['Location']
            break
        else:
            continue
    movement['distance']=distance
    movement['visit']=visit

Any way to make this faster? The main issue is this operation is a cartesian product, and any inserts will increase the complexity of the operation significantly.

Answer 1

You can export the pandas data directly to numpy for example like this:

loc_lat=locations['Latitude' ].to_numpy()
loc_lon=locations['Longitude'].to_numpy()
mov_lat=movements['Lat'      ].to_numpy()
mov_lon=movements['Lon'      ].to_numpy()

From now on there is no need to use loops to obtain results as you can rely on numpy working an entire arrays at once. This should give a great speedup over the approach using Python looping over dictionary values.

Check out following code example showing how to get an array with all pairs from two arrays:

import numpy as np
a = np.array([1,2,3])
b = np.array([4,5])
print( np.transpose([np.tile(a, len(b)), np.repeat(b,len(a))]) )
gives_as_print = """
[[1 4]
 [2 4]
 [3 4]
 [1 5]
 [2 5]
 [3 5]]"""