Python program to convert a list to a set based on a common element

When you need to group sublists that share common elements, you can convert them to sets and merge those with overlapping elements. This technique uses the union method to combine sets and recursion to handle multiple merges.

Example

Below is a demonstration of merging sublists based on common elements ?

def common_elem_set(my_set):
    for index, val in enumerate(my_set):
        for j, k in enumerate(my_set[index + 1:], index + 1):
            if val & k:  # Check if sets have common elements
                my_set[index] = val.union(my_set.pop(j))
                return common_elem_set(my_set)
    return my_set

my_list = [[18, 14, 12, 19], [9, 6, 2, 1], [54, 32, 21, 17], [18, 11, 13, 12]]

print("The list is :")
print(my_list)

my_set = list(map(set, my_list))

my_result = common_elem_set(my_set)

print("The result is :")
print(my_result)

The list is :
[[18, 14, 12, 19], [9, 6, 2, 1], [54, 32, 21, 17], [18, 11, 13, 12]]
The result is :
[{11, 12, 13, 14, 18, 19}, {9, 2, 6, 1}, {32, 17, 21, 54}]

How It Works

The algorithm follows these steps ?

• Convert each sublist to a set using map(set, my_list)

• Compare each set with all subsequent sets using nested loops

• Use the & operator to check for common elements between sets

• When common elements are found, merge the sets using union()

• Remove the merged set and recursively process the updated list

• Continue until no more merges are possible

Alternative Approach Using While Loop

Here's a non-recursive version that's easier to understand ?

def merge_common_sets(data):
    sets_list = [set(sublist) for sublist in data]
    
    merged = True
    while merged:
        merged = False
        for i in range(len(sets_list)):
            for j in range(i + 1, len(sets_list)):
                if sets_list[i] & sets_list[j]:  # Common elements found
                    sets_list[i] = sets_list[i].union(sets_list[j])
                    sets_list.pop(j)
                    merged = True
                    break
            if merged:
                break
    
    return sets_list

my_list = [[18, 14, 12, 19], [9, 6, 2, 1], [54, 32, 21, 17], [18, 11, 13, 12]]
result = merge_common_sets(my_list)

print("Original list:", my_list)
print("Merged sets:", result)

Original list: [[18, 14, 12, 19], [9, 6, 2, 1], [54, 32, 21, 17], [18, 11, 13, 12]]
Merged sets: [{11, 12, 13, 14, 18, 19}, {1, 2, 6, 9}, {17, 21, 32, 54}]

Key Points

• The & operator returns the intersection of two sets

• The union() method combines all elements from both sets

• Recursion ensures all possible merges are performed

• Sets automatically handle duplicate removal

Conclusion

This approach efficiently groups sublists with shared elements by converting them to sets and using set operations. The recursive method ensures all possible merges are completed, resulting in disjoint groups.