Python - Minimum in each record value list

When working with nested lists in Python, finding the minimum value in each sublist is a common task. This article explores three different approaches to extract minimum values from each record in a list of lists.

Understanding the Problem

Given a list containing multiple sublists, we need to find the minimum value from each sublist. For example, if we have [[8,10,12], [12, 14, 16], [17, 18, 19]], the minimum values are 8, 12, and 17 respectively, giving us the result [8, 12, 17].

Method 1: Using List Comprehension with min()

The most Pythonic approach uses list comprehension combined with the built-in min() function ?

record = [[81, 102, 123], [124, 145, 166], [177, 188, 199]]

# Find minimum value in each sublist
min_values = [min(sublist) for sublist in record]

print("Minimum values:", min_values)

Minimum values: [81, 124, 177]

Method 2: Using a For Loop

A traditional iterative approach using a for loop to traverse each sublist ?

record = [[81, 102, 123], [124, 145, 166], [177, 188, 199]]

# Initialize empty list to store minimum values
min_items = []

# Iterate through each sublist
for sublist in record:
    min_item = min(sublist)
    min_items.append(min_item)

print("Minimum values:", min_items)

Minimum values: [81, 124, 177]

Method 3: Using map() Function

The map() function applies min() to each sublist and returns an iterator ?

record = [[81, 102, 123], [124, 145, 166], [177, 188, 199]]

# Use map to apply min function to each sublist
min_items = list(map(min, record))

print("Minimum values:", min_items)

Minimum values: [81, 124, 177]

Working with Mixed Data Types

Here's an example with unsorted sublists containing different values ?

mixed_record = [[25, 10, 30], [5, 18, 2], [100, 50, 75]]

# Using list comprehension
result = [min(sublist) for sublist in mixed_record]

print("Original data:", mixed_record)
print("Minimum values:", result)

Original data: [[25, 10, 30], [5, 18, 2], [100, 50, 75]]
Minimum values: [10, 2, 50]

Comparison of Methods

Time Complexity

All three methods have a time complexity of O(n × m), where n is the number of sublists and m is the average length of each sublist. The space complexity is O(n) for storing the result list.

Conclusion

List comprehension with min() is the most Pythonic and efficient approach for finding minimum values in each sublist. Use the for loop method when you need additional processing logic, and map() for functional programming style.