Python: Create a dictionary with the unique values of a list as keys and their frequencies as the values

Last update on June 28 2025 12:43:29 (UTC/GMT +8 hours)

Frequency Dictionary from List

Write a Python program to create a dictionary with the unique values of a given list as keys and their frequencies as values.

• Use collections.defaultdict() to store the frequencies of each unique element.
• Use dict() to return a dictionary with the unique elements of the list as keys and their frequencies as the values.

Sample Solution:

Python Code:

# Import the 'defaultdict' class from the 'collections' module to create a dictionary with default values.
from collections import defaultdict

# Define a function 'frequencies' that takes a list 'lst' as input.
def frequencies(lst):
    # Create an empty dictionary with default integer values.
    freq = defaultdict(int)
    
    # Iterate over the elements 'val' in the input list 'lst'.
    for val in lst:
        # Increase the count of the element 'val' in the dictionary by 1.
        freq[val] += 1
    
    # Convert the defaultdict to a regular dictionary and return the result.
    return dict(freq)

# Call the 'frequencies' function with a list of strings to count the frequency of each string.
# Print the result.
print(frequencies(['a', 'b', 'f', 'a', 'c', 'e', 'a', 'a', 'b', 'e', 'f']))

# Call the 'frequencies' function again with a list of integers to count the frequency of each integer.
# Print the result.
print(frequencies([3, 4, 7, 5, 9, 3, 4, 5, 0, 3, 2, 3]))

Sample Output:

{'a': 4, 'b': 2, 'f': 2, 'c': 1, 'e': 2}
{3: 4, 4: 2, 7: 1, 5: 2, 9: 1, 0: 1, 2: 1}

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to create a frequency dictionary from a list of words, ignoring case and punctuation.
• Write a Python program to generate a frequency dictionary from a list of numbers and then filter out keys that occur only once.
• Write a Python program to compute the frequency dictionary of a list containing mixed data types, ensuring type-specific counting.
• Write a Python program to build a frequency dictionary from a list and then output the most and least frequent elements.

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