Python: Group a sequence of key-value pairs into a dictionary of lists

Last update on March 28 2025 12:55:59 (UTC/GMT +8 hours)

35. Group a Sequence of Key-Value Pairs into a Dictionary of Lists

Write a Python program to group a sequence of key-value pairs into a dictionary of lists.

Sample Solution:

Python Code:

# Import the defaultdict class from the collections module
from collections import defaultdict

# Create a list 'class_roll' containing tuples with class names and roll numbers
class_roll = [('v', 1), ('vi', 2), ('v', 3), ('vi', 4), ('vii', 1)]

# Create a defaultdict 'd' to store lists of roll numbers for each class
d = defaultdict(list)

# Loop through the tuples in 'class_roll'
for k, v in class_roll:
    # Append the roll number 'v' to the list associated with class 'k' in 'd'
    d[k].append(v)

# Sort the items (key-value pairs) in 'd' and print the result
print(sorted(d.items())) 

Sample Output:

[('v', [1, 3]), ('vi', [2, 4]), ('vii', [1])]

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to group a list of tuples into a dictionary where each key maps to a list of corresponding values using collections.defaultdict.
• Write a Python program to iterate through a list of key-value pairs and construct a dictionary of lists manually.
• Write a Python program to use dictionary comprehension to create a grouped dictionary from a list of tuples.
• Write a Python program to implement a function that returns a dictionary of lists from a given list of key-value pairs, preserving insertion order.

Python Code Editor:

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