#0093

Invert Dictionary to List Values

MediumPython25 min20 XP

Problem

Given a dictionary, return a new dictionary where each original value maps to a sorted list of keys that had that value.

Why This Matters

Inverting mappings is common in indexing, grouping, lookup table cleanup, and feature engineering.

Function Signature

def invert_to_groups(mapping):

Examples

Example 1

Input{"a": 1, "b": 2, "c": 1}

Output{1: ["a", "c"], 2: ["b"]}

Keys a and c shared value 1, so they are grouped together.

Constraints

Return the exact structure requested.
Handle the edge cases mentioned in the prompt.
Prefer clear logic over clever one-liners.

CodePython

def invert_to_groups(mapping):
    """
    Input example: {"a": 1, "b": 2, "c": 1}
    Return: {1: ["a", "c"], 2: ["b"]}
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return {}

def invert_to_groups(mapping):
    """
    Input example: {"a": 1, "b": 2, "c": 1}
    Return: {1: ["a", "c"], 2: ["b"]}
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return {}

Visible browser tests run here when available.

Testcases1 visible / 3 hidden categories

Core example

Input{"a": 1, "b": 2, "c": 1}

Expected{1: ["a", "c"], 2: ["b"]}

Keys a and c shared value 1, so they are grouped together.

Hidden Test Categories

empty dictall same valueall unique values