How to calculate variance in Pandas

Here’s how to calculate variance in Pandas.

How to calculate variance in Pandas

To calculate a variance in Pandas just use a var method which Pandas is offering to you.

import pandas as pd

my_df = pd.DataFrame({"my_column1": [9, 2, 3, 5],
                     "my_column2": [3, 7, 6, 4],
                      "my_column3": [4, 8, 8, 8]})

print(f'The variance of columns:\n{my_df.var()}')

The var method calculates the sample variance by default, which is an unbiased estimator of the population variance. The sample variance is calculated as the average of the squared differences between each value in the column and the mean of the column.

The variance of columns:
   my_column1  my_column2  my_column3
0           9           3           4
1          11          10          12
2          14          16          20
3          19          20          28

If you want to calculate the population variance, you can set the ddof parameter to 0:

variance = df['column_name'].var(ddof=0)

The ddof parameter stands for degrees of freedom and is used to adjust the denominator of the variance calculation for sample variance (ddof=1) or population variance (ddof=0).

It is important to understand the difference between sample variance and population variance and to set the ddof parameter appropriately when calculating the variance.

For more details see the documentation of var function.