How To Get All Subsets Of A List In Python

In this tutorial, we will learn how to get all the subsets of a list in Python. This is useful when you want to perform analysis, generate combinations, or find the power set of a list of elements.

We will discuss two methods to achieve this: first, by using a manual approach with loops, and second, by using the built-in itertools.chain and itertools.combinations functions.

Method 1: Using Loops

The first approach involves using a loop to iterate through the list and generate all possible subsets. By doing this, we will be creating the list of subsets step by step. Here’s a breakdown of the steps:

  1. Initialize an empty list, result, which will store the subsets.
  2. Add an empty subset to the result list.
  3. Iteratively go through each element in the input list.
  4. For each element, generate new subsets by adding it to the existing subsets in the result list.
  5. Add these new subsets to the result list.

Now, let’s see the code implementation:

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def get_all_subsets(input_list):
    result = [[]]
 
    for elem in input_list:
        new_subsets = [subset + [elem] for subset in result]
        result.extend(new_subsets)
 
    return result

Let’s test this function on an example input list:

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input_list = [1, 2, 3]
subsets = get_all_subsets(input_list)
print(subsets)

Output:[[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]
We can see that the function generated all possible subsets, including the empty set and the input list itself.

Method 2: Using itertools.chain and itertools.combinations

The second approach involves using the built-in Python library itertools to generate the subsets. The main advantage of using itertools is that it is more efficient in terms of both memory usage and computation time.

Here’s a step-by-step breakdown of the process:

  1. Import itertools.chain and itertools.combinations functions.
  2. Initialize an empty list, result, which will store the subsets.
  3. Iterate through the range from 0 to the length of the input list.
  4. For each number in the range, find all possible combinations using the combinations function.
  5. Add the combinations to the result list using the chain function.

Now, let’s see the code implementation:

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from itertools import chain, combinations
 
def get_all_subsets(input_list):
    result = list(chain.from_iterable(combinations(input_list, r) for r in range(len(input_list) + 1)))
    return result

Let’s test this function on an example input list:

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input_list = [1, 2, 3]
subsets = get_all_subsets(input_list)
print(subsets)

Output

[(), (1,), (2,), (3,), (1, 2), (1, 3), (2, 3), (1, 2, 3)]

We can see that the function generated all possible subsets in the form of tuples. We can easily convert them to lists if needed.

Conclusion

In this tutorial, we covered two methods to get all the subsets of a list in Python. The first approach was a manual implementation using loops. The second approach made use of the built-in itertools library to generate combinations more efficiently. Both methods have their merits and can be used based on your requirements and situation.