How to "inverse" list in python? Like Inverse Function

Question

I have some complicated function called dis(x), which returns a number.

I am making two lists called let's say ,,indices'' and ,,values''. So what I do is following:

for i in np.arange(0.01,4,0.01):
    values.append(dis(i))
    indices.append(i)

So i have following problem, how do i find some index j (from indices), which dis(j) (from values) is closest to some number k.

Answer 1

Combination of enumerate and the argmin function in numpy will do the job for you.

import numpy as np

values = []
indices = []
def dis(x):
    return 1e6*x**2

for i in np.arange(0.01,4,0.01):
    values.append(dis(i))
    indices.append(i)
target = 10000


closest_index = np.argmin([np.abs(x-target) for x in values])
print(closest_index)