Problem: Given a list of lists representing a data matrix with n rows and m columns. How to sum over the columns of this matrix? In this article, you’re going to learn different ways to accomplish this in Python. Let’s ensure that you’re on the same page. Here’s a graphical representation of the list of … Read more
Problem: You have a list of lists and you want to calculate the average of the different columns. Example: Given the following list of lists with four rows and three columns. You want to have the average values of the three columns: There are three methods that solve this problem. You can play with them … Read more
Short answer: You can remove all empty lists from a list of lists by using the list comprehension statement [x for x in list if x] to filter the list. In the following, you’ll learn about the two methods using list comprehension and the filter() function to remove all empty lists from a list of … Read more
[20-SEC SUMMARY] Given a list of list stored in variable lst. To flatten a list of lists, use the list comprehension statement [x for l in lst for x in l]. To modify all elements in a list of lists (e.g., increment them by one), use a list comprehension of list comprehensions [[x+1 for x … Read more
If you’re in a hurry, here’s the short answer: Use the list comprehension statement [list(x) for x in tuples] to convert each tuple in tuples to a list. This also works for a list of tuples with a varying number of elements. But there’s more to it, and studying the three main methods to achieve … Read more
If you’re in a hurry, here’s the short answer: use the list comprehension statement [tuple(x) for x in list] to convert each element in your list to a tuple. This works also for list of lists with varying number of elements. But there’s more to it and studying the two main methods to achieve the … Read more
For some applications, it’s quite useful to convert a list of lists into a dictionary. Databases: List of list is table where the inner lists are the database rows and you want to assign each row to a primary key in a new dictionary. Spreadsheet: List of list is two-dimensional spreadsheet data and you want … Read more
Say, you want to convert a list of lists lst=[[1, 2], [3, 4]] into a single list [1, 2, 3, 4]. How to achieve this? There are different options: List comprehension [x for l in lst for x in l] assuming you have a list of lists lst. Unpacking [*lst[0], *lst[1]] assuming you have a … Read more
[Spoiler] Which function filters a list faster: filter() vs list comprehension? For large lists with one million elements, filtering lists with list comprehension is 40% faster than the built-in filter() method. To answer this question, I’ve written a short script that tests the runtime performance of filtering large lists of increasing sizes using the filter() … Read more
How can you filter a list in Python using an arbitrary condition? The most Pythonic and most performant way is to use list comprehension [x for x in list if condition] to filter all elements from a list. Filter with List Comprehension The most Pythonic way of filtering a list—in my opinion—is the list comprehension … Read more
In this article, you’ll learn how to filter a list of dictionaries. So let’s get started! Short answer: The list comprehension statement [x for x in lst if condition(x)] creates a new list of dictionaries that meet the condition. All dictionaries in lst that don’t meet the condition are filtered out. You can define your … Read more
This is a tutorial video from my new book “Python One-Liners” with NoStarch press (San Francisco 2020). Grab your Python One-Liner Superpower now! (Amazon Link) Here’s the code that shows you how to sample a two-dimensional Python list—including only every other list element in the resulting two-dimensional Python list. All of this happens in a … Read more