*28*

You can use the following basic syntax to group rows by year in a pandas DataFrame:

df.groupby(df.your_date_column.dt.year)['values_column'].sum()

This particular formula groups the rows by date in **your_date_column** and calculates the sum of values for the **values_column** in the DataFrame.

Note that the **dt.year()** function extracts the year from a date column in pandas.

The following example shows how to use this syntax in practice.

**Example: How to Group by Year in Pandas**

Suppose we have the following pandas DataFrame that shows the sales made by some company on various dates:

**import pandas as pd
#create DataFrame
df = pd.DataFrame({'date': pd.date_range(start='1/1/2020', freq='3m', periods=10),
'sales': [6, 8, 9, 11, 13, 8, 8, 15, 22, 9],
'returns': [0, 3, 2, 2, 1, 3, 2, 4, 1, 5]})
#view DataFrame
print(df)
date sales returns
0 2020-01-31 6 0
1 2020-04-30 8 3
2 2020-07-31 9 2
3 2020-10-31 11 2
4 2021-01-31 13 1
5 2021-04-30 8 3
6 2021-07-31 8 2
7 2021-10-31 15 4
8 2022-01-31 22 1
9 2022-04-30 9 5**

**Related:** How to Create a Date Range in Pandas

We can use the following syntax to calculate the sum of sales grouped by year:

#calculate sum of sales grouped by year df.groupby(df.date.dt.year)['sales'].sum() date 2020 34 2021 44 2022 31 Name: sales, dtype: int64

Hereâ€™s how to interpret the output:

- The total sales made during 2020 was
**34**. - The total sales made during 2021 was
**44**. - The total sales made during 2022 was
**31**.

We can use similar syntax to calculate the max of the sales values grouped by year:

#calculate max of sales grouped by year df.groupby(df.date.dt.year)['sales'].max() date 2020 11 2021 15 2022 22 Name: sales, dtype: int64

We can use similar syntax to calculate any value weâ€™d like grouped by the year value of a date column.

**Note**: You can find the complete documentation for the GroupBy operation in pandas here.

**Additional Resources**

The following tutorials explain how to perform other common operations in pandas:

Pandas: How to Calculate Cumulative Sum by Group

Pandas: How to Count Unique Values by Group

Pandas: How to Calculate Correlation By Group