CODEWITHSUNDEEP
pythonscipyeuclidean-distance
An student
An student

Reputation: 392

Finding distance between elements of two different list

The code below finds the Euclidean distance between each element of list a and each element of list b.

from scipy.spatial import distance
a = [[1, 2, 3], [4, 5, 6]]
b = [[10, 20]]

Final_distance = []
for i in [j for sub in a for j in sub]:
    for k in [m for t in b for m in t]:
        dist = distance.euclidean(i, k)
        Final_distance.append(dist)
print(Final_distance)

The output is

[9.0, 19.0, 8.0, 18.0, 7.0, 17.0, 6.0, 16.0, 5.0, 15.0, 4.0, 14.0]

But for very large list it is taking very long time. Is there a way to reduce the time complexity of the above code?

Upvotes: 3

Views: 930

Answers (1)

sacuL
sacuL

Reputation: 51335

Since your euclidian distances are on scalars, it's equivalent to the absolute value between each point. So you can repeat your arrays in the appropriate order using np.repeat and np.tile, and just subtract your arrays from one another:

import numpy as np

a = [[1, 2, 3], [4, 5, 6]]
b = [[10, 20]]

a1 = np.array(a).flatten()
b1 = np.array(b).flatten()

Final_distance = np.abs(np.subtract(np.repeat(a1, len(b1)), np.tile(b1, len(a1))))

Which returns:

array([ 9, 19,  8, 18,  7, 17,  6, 16,  5, 15,  4, 14])

Upvotes: 3

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