Python | Indices list of matching element from other list

Last Updated : 10 Oct, 2019

Sometimes, while working with Python list, we have a problem in which we have to search for a element in list. But this can be extended to a list and need to find the exact places where elements occur in other list. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using loop + count()
This is the brute method to perform this task. In this we can just count the occurrence of an element in other list and if we find it, then we add it’s index to the result list.

# Python3 code to demonstrate working of
# Indices list of matching element from other list
# Using loop + count()
  
# initializing lists
test_list1 = [5, 7, 8, 9, 10, 11]
test_list2 = [8, 10, 11]
  
# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))
  
# Indices list of matching element from other list
# Using loop + count()
res = []
i = 0
while (i < len(test_list1)):
    if (test_list2.count(test_list1[i]) > 0):
        res.append(i)
    i += 1
  
# printing result 
print("The matching element Indices list : " + str(res))

Output :

The original list 1 is : [5, 7, 8, 9, 10, 11]
The original list 2 is : [8, 10, 11]
The matching element Indices list : [2, 4, 5]

Method #2 : Using list comprehension + set() + enumerate()
The combination of above functions can be used to perform the task. In these we just convert the list to set and then check for index and value together for existence using enumerate() and append the index if found.

# Python3 code to demonstrate working of
# Indices list of matching element from other list
# Using list comprehension + set() + enumerate()
  
# initializing lists
test_list1 = [5, 7, 8, 9, 10, 11]
test_list2 = [8, 10, 11]
  
# printing original lists
print("The original list 1 is : " + str(test_list1))
print("The original list 2 is : " + str(test_list2))
  
# Indices list of matching element from other list
# Using list comprehension + set() + enumerate()
temp = set(test_list2)
res = [i for i, val in enumerate(test_list1) if val in temp]
  
# printing result 
print("The matching element Indices list : " + str(res))

Output :

The original list 1 is : [5, 7, 8, 9, 10, 11]
The original list 2 is : [8, 10, 11]
The matching element Indices list : [2, 4, 5]

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