Want to calculate the variance of a column in your Pandas DataFrame?
In case you’ve attended your last statistics course a few years ago, let’s quickly recap the definition of variance: it’s the average squared deviation of the list elements from the average value.
You can calculate the variance of a Pandas DataFrame by using the pd.var() function that calculates the variance along all columns. You can then get the column you’re interested in after the computation.
import pandas as pd
# Create your Pandas DataFrame
d = {'username': ['Alice', 'Bob', 'Carl'],
'age': [18, 22, 43],
'income': [100000, 98000, 111000]}
df = pd.DataFrame(d)
print(df)
Your DataFrame looks like this:
| username | age | income | |
| 0 | Alice | 18 | 100000 |
| 1 | Bob | 22 | 98000 |
| 2 | Carl | 43 | 111000 |
Here’s how you can calculate the variance of all columns:
print(df.var())
The output is the variance of all columns:
age 1.803333e+02 income 4.900000e+07 dtype: float64
To get the variance of an individual column, access it using simple indexing:
print(df.var()['age']) # 180.33333333333334
Together, the code looks as follows. Use the interactive shell to play with it!
Where to Go From Here?
Before you can become a data science master, you first need to master Python. Join my free Python email course and receive your daily Python lesson directly in your INBOX. It’s fun!
Join The World’s #1 Python Email Academy [+FREE Cheat Sheets as PDF]
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 that has taught exponential skills to millions of coders worldwide. He’s the author of the best-selling programming books Python One-Liners (NoStarch 2020), The Art of Clean Code (NoStarch 2022), and The Book of Dash (NoStarch 2022). Chris also coauthored the Coffee Break Python series of self-published books. He’s a 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.