Find duplicates within and outside nested list in python

user_13370214 0
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I have a list s:

s=[[1,2,1],[2,2,1],[1,2,1]]

Case 1: Remove the duplicate groups in the list

Case 2: Remove the duplicate values within the groups

Desired Result:

Case 1 : [[1,2,1],[2,2,1]]
Case 2 : [[1,2],[2,1],[1,2]]

I tried using the list(set(s)) but it throws up an error:

unhashable type: 'list'

set for-loop list python
2 Answers

IIUC,

Case 1:

Convert the lists to tuple for hashing, then apply a set on the list of tuples to remove the duplicates. Finally, convert back to lists.

out1 = list(map(list, set(map(tuple, s))))
# [[1, 2, 1], [2, 2, 1]]
Case 2:

For each sublist, remove the duplicates while keeping order with conversion to dictionary keys (that are unique), then back to list:

out2 = [list(dict.fromkeys(l)) for l in s]
# [[1, 2], [2, 1], [1, 2]]
user_163434640

You need to know that it's not possible in Python to have a set of lists. The reason is that lists are not hashable. The simplest way to do your task in the first case is to use a new list of lists without duplicates such as below:

temp_list = []
for each_element in [[1,2,1],[2,2,1],[1,2,1]]:
    if each_element not in temp_list:
        temp_set.append(each_element)
print(temp_list)

The output:

[[1, 2, 1], [2, 2, 1]]

The case2 is more simple:

temp_list = []
for each_element in [[1,2,1],[2,2,1],[1,2,1]]:
    temp_list.append(list(set(each_element)))
print(temp_list)

And this is the output:

[[1, 2], [1, 2], [1, 2]]

However these codes are not the pythonic way of doing things, they are very simple to be understood by beginners.

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