Condensed matrix function to find pairs

Question

For a set of observations:

[a1,a2,a3,a4,a5]

their pairwise distances

d=[[0,a12,a13,a14,a15]
   [a21,0,a23,a24,a25]
   [a31,         


        

Answer 1

Here's another solution:

import numpy as np

def f(c,n):
    tt = np.zeros_like(c)
    tt[n] = 1
    return tuple(np.nonzero(squareform(tt))[0])