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I am writing a code to calculate the shortest distance between two sets of points. Essentially, I have created a csv with a bunch of locations in coordinates, and a second csv with a second bunch of locations in coordinates. For example, the coordinates in list A could be (50, -10), (60, 70), (40, -19) and in list B, it could be (40, 87), (60, 90), (23, 20). Everything I have found online to help me calculates between a list and a single point: this won't work for me.

So far I am able to calculate the distance between all the points (so between A1 and B1, A1 and B2, A1 and B3, A2 and B1, etc). That's fine, but what I want is the minimum distance from point 1 in list A to ANY point in list B. Essentially, what position in list B is closest to each point in list A?

I'm trying to find a way to run it so it checks A1 against B1, B2, B3 etc, and then comes back with the shortest distance being x miles between A1 and B3, for example.

What I have so far is below:

import pandas as pd
import geopy.distance

df = pd.read_csv('AirportCoords.csv')
df2 = pd.read_csv('HotelCoords.csv')

for i,row in df2.iterrows():
coordinate = row.lat, row.long
for i,row in df.iterrows():
    coordinate2 = row.latitude, row.longitude

    distance = geopy.distance.geodesic(coordinate, coordinate2).km
    print(distance)
eyllanesc
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TeenySceney
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1 Answers1

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You're talking about comparing every element of A to every element of B, this implies that you should have a nested loop, but your example code actually has 2 loops in sequence.

import pandas as pd
import geopy.distance

df = pd.read_csv('AirportCoords.csv')
df2 = pd.read_csv('HotelCoords.csv')


for i,row in df.iterrows(): # A
    a = row.latitude, row.longitude
    distances = []
    for j,row2 in df2.iterrows(): # B
        b = row2.lat, row2.long
        distances.append(geopy.distance.geodesic(a, b).km)

    min_distance = min(distances)
    min_index = distances.index(min_distance)

    print("A", i, "is closest to B", min_index, min_distance, "km")
Hymns For Disco
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  • thank you! A very foolish mistake but now I understand nesting loops, so I can't thank you enough. – TeenySceney Nov 13 '19 at 20:14
  • You're welcome. If this fully answered your question could you mark it as the accepted answer? That way the question will be shown as resolved – Hymns For Disco Nov 13 '19 at 20:20