## Problem Formulation

π¬ **Programming Challenge**: Given a dictionary where the values are lists of varying sizes. Find and return the shortest list!

Here’s an example:

d = {1: [1, 2, 3], 2: [1, 2], 3: [1], 4: [1, 2, 3, 4]} # Goal: [1]

Also, you’ll learn how to solve a variant of this challenge.

π¬ **Bonus challenge**: Find only the *key* that is associated with the shortest list in the dictionary.

Here’s an example:

d = {1: [1, 2, 3], 2: [1, 2], 3: [1], 4: [1, 2, 3, 4]} # Goal: 1

So without further ado, let’s get started!

## Method 1: min(lst, key=len)

Use Pythonβs built-in `min()`

function with a key argument to find the shortest list from the dictionary values. Call `min(d.values(), key=len)`

to return the shortest list in `d.values()`

using the built-in `len()`

function to associate the weight of each list, so that the shortest list will be the minimum.

Here’s an example:

d = {1: [1, 2, 3], 2: [1, 2], 3: [1], 4: [1, 2, 3, 4]} print(min(d.values(), key=len)) # [1]

A beautiful one-liner solution, isn’t it? π Let’s have a look at a slight variant to check the *key *of the shortest list instead.

π** Recommended Tutorial**: Python Find Longest List in Dict

## Method 2: len(min(lst, key=len))

To get the key mapping to the shortest list value in a dictionary, use `min(d, key=lambda x: len(d[x]))`

.

**Explanation**: You set the key argument of `min()`

to a lambda function that maps each dictionary key `x`

to the length of the associated value obtained with `len(d[x])`

. This way, you use the length of the mapped values as weights to determine the “minimum”, i.e., the shortest list.

π‘ **Note**: When you call `min(d)`

Python will automatically replace it with `min(d.keys())`

, so it iterates over the keys of the dictionary.

Here’s an analogous example:

d = {1: [1, 2, 3], 2: [1, 2], 3: [1], 4: [1, 2, 3, 4]} print(min(d, key=lambda x: len(d[x]))) # 1

The key with shortest list in the dictionary is `4`

.

π **Recommended Tutorial**: A Complete Guide to Python Dictionaries

## Method 4: Shortest List in Dict Values Using List Comprehension

You can also get the length of the shortest list from the dictionary values by combining a generator expression or list comprehension with the `min()`

function without key using the following expression: `min(len(val) for val in d.values())`

Like so:

d = {1: [1, 2, 3], 2: [1, 2], 3: [1], 4: [1, 2, 3, 4]} print(min(len(val) for val in d.values())) # 1

Note that this returns the length of the shortest list in the dict values, not the key or the list itself.

A good training effect can be obtained by studying the following tutorial on the topic—feel free to do so!

π **Training**: Understanding List Comprehension in Python

## Method 4: Naive For Loop

A not so Pythonic but still fine approach is to iterate over all key-value pairs in a `for`

loop, check their length using the `len()`

function, and compare it against the currently shortest list stored in a separate variable. After the termination of the loop, the variable contains the shortest list.

Here’s a simple example:

d = {1: [1, 2, 3], 2: [1, 2], 3: [1], 4: [1, 2, 3, 4]} # Initialize variables with dummy values k_min, v_min = -1, [] i = 0 for key,val in d.items(): if len(val) < len(v_min) or i==0: k_min, v_min = key, val i += i print("Shortest key and value:", str(k_min) + ',' + str(v_min)) # Shortest key and value: 3,[1]

So many lines of code! π I hate it.

## Summary

You have learned about four ways to find the shortest list and its length from a Python list of lists (nested list):

- Method 1: min(lst, key=len)
- Method 2: len(min(lst, key=len))
- Method 4: Shortest List in Dict Values Using List Comprehension
- Method 4: Naive For Loop

I hope you found the tutorial helpful. If you did, feel free to consider joining our community of likeminded coders—we do have lots of free training material!

π** Recommended Tutorial**: Python Find Longest List in List

While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.

To help students reach higher levels of Python success, he founded the programming education website Finxter.com. He’s author of the popular programming book Python One-Liners (NoStarch 2020), coauthor of the Coffee Break Python series of self-published books, computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.

His passions are writing, reading, and coding. But his greatest passion is to serve aspiring coders through Finxter and help them to boost their skills. You can join his free email academy here.