Search a value between indexes of an array in Python

Question

I have a sorted list(it contains more than 1000 cumulative elements). For example:

list = [1.236, 2.236, 5.1254, 9.125663, 9.9632, 15.1266, 18.254, 19.3315, 23.3265]

And I have a target number which is let's say 9.5. I want to find its position in list. So I want to see index 3rd and 4 (it should be between 3 (9.125663) and 4th (9.9632) indexes) as output without using a for loop.

Do you have an idea about it? Thank you.

just subtract your value from the list (with numpy) and look for the closest value to zero: check out [find-nearest-value-in-numpy-array](https://stackoverflow.com/questions/2566412/find-nearest-value-in-numpy-array) — Marc, Apr 21 '21 at 09:51

score 3 · Answer 1 · answered Apr 21 '21 at 10:00

There is bisect module for this:

import bisect

the_list = [1.236, 2.236, 5.1254, 9.125663, 9.9632, 15.1266, 18.254, 19.3315, 23.3265]
val = 9.5
pos = bisect.bisect(the_list, val)

to get

>>> pos
4

You can then use (pos-1, pos) as (3, 4) (might need to check edge cases).

(Side note: bisect.bisect is synonymous to bisect.bisect_right so the returned pos will be right to the val if it is already in the list, e.g. if val was 5.1254, pos would be 3).

Learn something everyday. This is a great answer! – Johnny John Boy Apr 21 '21 at 11:22 — Johnny John Boy, Apr 21 '21 at 11:22

score 2 · Answer 2 · answered Apr 21 '21 at 09:56

Used this link for the answer:

import numpy as np

def get_indices(array, value):
    array = np.array(array)

    # Subtract all values in array with value and get index of smallest value which would be the closest value
    idx = (np.abs(array - value)).argmin()

    #if closest value is greater than target value
    if(array[idx] > value):
        #+1 because you want "3rd and 4th" index, and python starts from 0
        print([idx+1, idx+2])

    #if closest value is lesser than target value
    elif(array[idx] < value):
        print([idx, idx+1])
    
    else:
        print([idx+1])

array = [1.236, 2.236, 5.1254, 9.125663, 9.9632, 15.1266, 18.254, 19.3315, 23.3265]
value = 9.5
get_indices(array, 9.5)  ## prints [3,4]
get_indices(array, 10.5) ## prints [4,5]

Search a value between indexes of an array in Python

2 Answers2