Python - Inter Matrix Grouping

Inter Matrix Grouping is a technique where elements from two lists are grouped based on matching first elements. When matches are found, the first element becomes a dictionary key, and the remaining elements form grouped values. Python provides several built-in functions like setdefault(), defaultdict(), and append() to implement this efficiently.

Understanding the Concept

Let's understand this with an example:

list1 = [[1, 2], [3, 4], [4, 5], [5, 6]]
list2 = [[5, 60], [1, 22], [4, 59], [3, 14]]

# Result: {1: [2, 22], 3: [4, 14], 4: [5, 59], 5: [6, 60]}

Here, keys 1, 3, 4, 5 appear in both lists, so their corresponding values are grouped together.

Method 1: Using setdefault() Function

The setdefault() method returns a key's value if it exists, or creates the key with a default value if it doesn't ?

def inter_matrix_grouping(list1, list2):
    result = {}
    for key, value in list1 + list2:
        result.setdefault(key, []).append(value)
    return result

list1 = [[20, 0], [40, 200], [60, 300]]
list2 = [[40, 500], [60, 50], [20, 100]]

result = inter_matrix_grouping(list1, list2)
print("Inter Matrix grouping result:")
print(result)

Inter Matrix grouping result:
{20: [0, 100], 40: [200, 500], 60: [300, 50]}

Method 2: Using defaultdict() Function

The defaultdict() automatically creates missing keys with default values, eliminating the need to check if a key exists ?

from collections import defaultdict

def inter_matrix_grouping(list1, list2):
    result = defaultdict(list)
    for key, value in list1 + list2:
        result[key].append(value)
    return dict(result)

list1 = [[20, 0], [40, 200], [60, 300]]
list2 = [[40, 500], [60, 50], [20, 100]]

result = inter_matrix_grouping(list1, list2)
print("Inter Matrix grouping result:")
print(result)

Inter Matrix grouping result:
{20: [0, 100], 40: [200, 500], 60: [300, 50]}

Method 3: Using Manual Dictionary Operations

This approach manually checks if keys exist and creates lists accordingly ?

def inter_matrix_grouping(list1, list2):
    merged_list = list1 + list2
    result = {}
    
    for key, value in merged_list:
        if key in result:
            result[key].append(value)
        else:
            result[key] = [value]
    
    return result

list1 = [[20, 0], [40, 200], [60, 300]]
list2 = [[40, 500], [60, 50], [20, 100]]

result = inter_matrix_grouping(list1, list2)
print("The result of Inter Matrix Grouping:")
print(result)

The result of Inter Matrix Grouping:
{20: [0, 100], 40: [200, 500], 60: [300, 50]}

Comparison

Conclusion

Inter Matrix Grouping efficiently combines data from multiple lists based on common keys. The defaultdict() approach offers the best performance and readability, while setdefault() provides a good balance for simpler use cases.