Suppose, I have a list of lists where multiple lists can have same elements. In my final output, I just want one list with the same element. An example is the following:

Input: A=[[1,2,0], [0,1,2], [2,1,0], [4,5,6], [6,5,4]]

Desired Output: $[[0,1,2], [4,5,6]]$

Can someone help me with an easy function for doing so? Thank you so much.

  • 2
    $\begingroup$ What about [[1, 2], [2, 3]]? $\endgroup$
    – greybeard
    Commented Mar 1, 2023 at 6:22
  • 3
    $\begingroup$ Your question is not clear. Please specify exactly what you want the output to be in general. One example is not a substitute for a general problem specification. "one list with the same element" is not clear. Same as what? You mention only one element, but the example shows multiple elements. $\endgroup$
    – D.W.
    Commented Mar 1, 2023 at 18:17
  • $\begingroup$ In fact, you are seeing your lists as (multi)sets. $\endgroup$
    – user16034
    Commented Jul 29, 2023 at 11:43

2 Answers 2


Sort every sublist, then sort the main list with lexicographical ordering. The duplicates will appear next to each other.

$$[[1,2,0], [6,5,4], [0,1,2], [2,1,0], [4,5,6]]$$ then $$[[0,1,2], [4,5,6], [0,1,2], [0,1,2], [4,5,6]]$$ then $$[[0,1,2], [0,1,2], [0,1,2], [4,5,6], [4,5,6]]$$


This appears to be an instance of the set cover problem. There is no efficient algorithm, but you can read about standard algorithms.

  • 4
    $\begingroup$ It could be that, or it could just be removal of duplicates. $\endgroup$
    – Pseudonym
    Commented Mar 1, 2023 at 5:34

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