How to Remove Duplicate Values from Dictionary in Python

To remove duplicate values from a dictionary in Python, you can create a new dictionary by iterating over the original and keeping only the first occurrence of each value using a set to track seen values. This is commonly done with a dictionary comprehension combined with a set to filter duplicates.

Syntax

You can remove duplicate values from a dictionary by creating a new dictionary using a dictionary comprehension. Use a set to keep track of values you have already seen and only add key-value pairs if the value is new.

General syntax:

seen = set()
new_dict = {k: v for k, v in original_dict.items() if v not in seen and (seen.add(v) or True)}

Here, seen.add(v) or True adds the value to the set and returns True so the condition passes.

python

seen = set()
new_dict = {k: v for k, v in original_dict.items() if v not in seen and (seen.add(v) or True)}

Example

This example shows how to remove duplicate values from a dictionary. The new dictionary keeps only the first key for each unique value.

python

original_dict = {'a': 1, 'b': 2, 'c': 1, 'd': 3, 'e': 2}
seen = set()
new_dict = {k: v for k, v in original_dict.items() if v not in seen and (seen.add(v) or True)}
print(new_dict)

Output

{'a': 1, 'b': 2, 'd': 3}

Common Pitfalls

One common mistake is trying to remove duplicates by just converting dictionary values to a set, which loses the keys and order.

Another mistake is not preserving the first occurrence of each value, which can lead to unexpected results.

python

original_dict = {'a': 1, 'b': 2, 'c': 1}
# Wrong: loses keys and order
unique_values = set(original_dict.values())
print(unique_values)

# Right: preserves keys and order
seen = set()
new_dict = {k: v for k, v in original_dict.items() if v not in seen and (seen.add(v) or True)}
print(new_dict)

Output

{1, 2}
{'a': 1, 'b': 2}

Quick Reference

• Use a set to track seen values.
• Use dictionary comprehension to build a new dictionary without duplicates.
• Preserve the first key for each unique value.
• Do not convert values directly to a set if you want to keep keys.

Key Takeaways

Use a set to track seen values when removing duplicates from a dictionary.

Dictionary comprehension helps create a new dictionary with unique values while preserving keys.

Preserve the first occurrence of each value to keep dictionary order and meaning.

Avoid converting dictionary values directly to a set if you want to keep keys.

This method works well for dictionaries with hashable values.