Python – Nearest occurrence between two elements in a List

Given a list and two elements, x and y find the nearest occurrence index of element x from element y.

Input : test_list = [2, 4, 5, 7, 8, 6, 3, 8, 7, 2, 0, 9, 4, 9, 4], x = 4, y = 6 
Output : 1 
Explanation : 4 is found at 1, 12 and 14th index, 6 is at 5th index, nearest is 1st index.

Input : test_list = [2, 4, 5, 7, 8, 6, 3, 8, 7, 2, 0, 9, 4, 9, 4], x = 7, y = 6 
Output : 3 
Explanation : 7 is found at 3rd and 8th index, 6 is at 5th index, nearest is 3rd index. 

Method : Using list comprehension + loop + index()

In this, we find all indices of y using list comprehension, and then get index of x using index(), post that loop is used to get index difference, the nearest index is returned as result.

Python3

# Python3 code to demonstrate working of
# Nearest occurrence of x from y in List
# Using list comprehension + loop + index()


# function to find index of nearest
# occurrence between two elements
def nearestOccurrenceIndex(test_list, x, y):

    # checking if both elements are present in list
    if x not in test_list or y not in test_list:
        return -1
    # getting indices of x
    x_idx = [idx for idx in range(len(test_list)) if test_list[idx] == x]

    # getting y index
    y_idx = test_list.index(y)

    # getting min_dist index
    min_dist = 1000000
    res = None
    for ele in x_idx:

        # checking for min ele, and updating index
        if abs(ele - y_idx) < min_dist:
            res = ele
            min_dist = abs(ele - y_idx)
    return res


# initializing list
input_list = [2, 4, 5, 7, 8, 6, 3, 8, 4, 2, 0, 9, 4, 9, 4]

# printing original list
print("The original list is : " + str(input_list))

# initializing x
x = 4

# initializing y
y = 6

# printing result
print("Minimum distance index: ", nearestOccurrenceIndex(input_list, x, y))

Output:

The original list is : [2, 4, 5, 7, 8, 6, 3, 8, 4, 2, 0, 9, 4, 9, 4] 
Minimum distance index:  8