Get Indices of Each Element of One List in Another List in Python

When it is required to get the indices of each element of one list in another list, a simple iteration and the enumerate attribute along with the ‘setdefault’ method is used.

It also uses list comprehension and the ‘get’ method is used.

Example

Below is a demonstration of the same −

my_list = [14, 52, 23, 47, 18, 23, 12, 54, 43, 22, 28, 13]

print("The list is :")
print(my_list)

my_list_2 = [17, 52, 13]
print("The second list is :")
print(my_list_2)

element_indices = dict()
for index, value in enumerate(my_list):
   element_indices.setdefault(value, []).append(index)

my_result = [element_indices.get(index, [None]) for index in my_list_2]

print("The result is :")
print(my_result)

Output

The list is :
[14, 52, 23, 47, 18, 23, 12, 54, 43, 22, 28, 13]
The second list is :
[17, 52, 13]
The result is :
[[None], [1], [11]]

Explanation

• A list of integers is defined and is displayed on the console.

• Another list of integers is defined and displayed on the console.

• An empty dictionary is created.

• The first list is iterated over using ‘enumerate’.

• The ‘setdefault’ method is used to give a value to the element.

• This is appended to the empty dictionary.

• A list comprehension is used to iterate over the elements and the ‘get’ method is used to get the index values for elements in the second index.

• This is stored in a list and is assigned to a variable.

• This list is displayed as the output on the console.