Given 2 lists, get all the indices of all occurrence of each element in list2 from list1.
Input : test_list = [4, 5, 3, 7, 8, 3, 2, 4, 3, 5, 8, 3], get_list = [7, 5, 4]
Output : [[3], [1, 9], [0, 7]]
Explanation : 5 is present at 1st and 9th index.Input : test_list = [4, 5, 3, 7, 8, 3, 2, 4, 3, 5, 8, 3], get_list = [7, 5, 8]
Output : [[3], [1, 9], [4, 10]]
Explanation : 8 is present at 4th and 10th index.
Method #1 : Using loop + setdefault()
In this, we perform the task of getting all the elements list grouped with their indices, and in 2nd run, get only the elements that are present in the other list.
Python3
# Python3 code to demonstrate working of # Multiple Indices from list elements # Using setdefault() + loop # initializing list test_list = [4, 5, 3, 7, 8, 3, 2, 4, 3, 5, 8, 3] # printing original list print("The original list is : " + str(test_list)) # initializing get_list get_list = [7, 5, 3] # getting all elements indices ele_indices = dict() for idx, val in enumerate(test_list): ele_indices.setdefault(val, []).append(idx) # filtering only required elements res = [ele_indices.get(idx, [None]) for idx in get_list] # printing result print("Filtered Indices of elements in list 1 : " + str(res)) |
The original list is : [4, 5, 3, 7, 8, 3, 2, 4, 3, 5, 8, 3] Filtered Indices of elements in list 1 : [[3], [1, 9], [2, 5, 8, 11]]
Method #2 : Using list comprehension + enumerate()
In this we use a nested loop, to get all the indices, and then filter in case of presence in another list.
Python3
# Python3 code to demonstrate working of # Multiple Indices from list elements # Using list comprehension + enumerate() # initializing list test_list = [4, 5, 3, 7, 8, 3, 2, 4, 3, 5, 8, 3] # printing original list print("The original list is : " + str(test_list)) # initializing get_list get_list = [7, 5, 3] # enumerate() used to get idx, val simultaneously res = [([idx for idx, val in enumerate(test_list) if val == sub] if sub in test_list else [None]) for sub in get_list] # printing result print("Indices of elements in list 1 : " + str(res)) |
The original list is : [4, 5, 3, 7, 8, 3, 2, 4, 3, 5, 8, 3] Indices of elements in list 1 : [[3], [1, 9], [2, 5, 8, 11]]
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