Finding the Summation of Nested Dictionary Values in Python

Sometimes we need to sum up values in nested dictionaries. In this article, we'll explore different approaches to find the summation of nested dictionary values using Python.

Understanding the Problem

A nested dictionary is a dictionary that contains other dictionaries as values. Our goal is to find and sum all numeric values within these nested structures. This is useful for aggregating data in hierarchical formats like JSON or configuration files.

Method 1: Sum All Nested Dictionary Values

This approach recursively traverses the nested dictionary and sums all numeric values it encounters ?

Algorithm

• Step 1 Define a function that takes a nested dictionary as input

• Step 2 Initialize a sum variable to store the total

• Step 3 Iterate through all values in the dictionary

• Step 4 If a value is numeric, add it to the sum

• Step 5 If a value is another dictionary, recursively call the function

• Step 6 Return the total sum

Example

# Function to get the summation of all values
def summation_values(the_dictionary):
    total_sum = 0
    for value in the_dictionary.values():
        if isinstance(value, int):
            total_sum += value
        elif isinstance(value, dict):
            total_sum += summation_values(value)
    return total_sum

# Input nested dictionary
nested_dict = {
    'apple': 10,
    'banana': {
        'cucumber': 12,
        'pineapple': {
            'orange': 23,
            'mango': 14
        }
    },
    'guava': 16
}

# Calculate the sum
result = summation_values(nested_dict)
print("The summation of nested dictionary values:", result)

The summation of nested dictionary values: 75

Complexity

The time complexity is O(N), where N is the total number of key-value pairs across all nested levels. The space complexity is O(D) due to recursion depth D.

Method 2: Sum Values with Identical Keys

This approach groups values by their keys across different sub-dictionaries and sums values that share the same key name ?

Example

# Initialize the nested dictionary
the_nested_dict = {
    'apple': {'red': 4, 'yellow': 5, 'green': 8},
    'guava': {'red': 8, 'white': 10},
    'banana': {'yellow': 19, 'green': 10}
}

# Initialize empty dictionary to store sums
sum_values = {}

# Iterate through each sub-dictionary
for subdict in the_nested_dict.values():
    for key, value in subdict.items():
        sum_values[key] = value + sum_values.get(key, 0)

# Display results
print("The summation values:", sum_values)

The summation values: {'red': 12, 'yellow': 24, 'green': 18, 'white': 10}

Complexity

The time complexity is O(N × M), where N is the number of main dictionary entries and M is the average number of key-value pairs in sub-dictionaries.

Method 3: Using Collections.defaultdict

We can simplify the identical keys approach using defaultdict ?

from collections import defaultdict

# Initialize the nested dictionary
the_nested_dict = {
    'fruits': {'apple': 5, 'banana': 3},
    'vegetables': {'carrot': 2, 'apple': 1},  # 'apple' appears again
    'grains': {'rice': 10, 'banana': 2}       # 'banana' appears again
}

# Use defaultdict to automatically initialize missing keys
sum_values = defaultdict(int)

for subdict in the_nested_dict.values():
    for key, value in subdict.items():
        sum_values[key] += value

# Convert back to regular dict and display
result = dict(sum_values)
print("Summation using defaultdict:", result)

Summation using defaultdict: {'apple': 6, 'banana': 5, 'carrot': 2, 'rice': 10}

Comparison

Conclusion

Use recursive summation when you need the total of all values in nested dictionaries. Use the identical keys approach when you want to group and sum values by their key names across different sub-dictionaries.