You can use the following basic syntax to group rows by day in a pandas DataFrame:
df.groupby(df.your_date_column.dt.day)['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.day() function extracts the day from a date column in pandas.
The following example shows how to use this syntax in practice.
Example: How to Group by Day 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='8h', 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 2020-01-01 00:00:00 6 0
1 2020-01-01 08:00:00 8 3
2 2020-01-01 16:00:00 9 2
3 2020-01-02 00:00:00 11 2
4 2020-01-02 08:00:00 13 1
5 2020-01-02 16:00:00 8 3
6 2020-01-03 00:00:00 8 2
7 2020-01-03 08:00:00 15 4
8 2020-01-03 16:00:00 22 1
9 2020-01-04 00:00:00 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 day:
#calculate sum of sales grouped by day
df.groupby(df.date.dt.day)['sales'].sum()
date
1 23
2 32
3 45
4 9
Name: sales, dtype: int64
Here’s how to interpret the output:
- The total sales made on January 1st was 23.
- The total sales made on January 2nd was 32.
- The total sales made on January 3rd was 45.
- The total sales made on January 4th was 9.
We can use similar syntax to calculate the max of the sales values grouped by month:
#calculate max of sales grouped by day
df.groupby(df.date.dt.day)['sales'].max()
date
1 9
2 13
3 22
4 9
Name: sales, dtype: int64
We can use similar syntax to calculate any value we’d like grouped by the day 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:
How to Group by Week in Pandas
How to Group by Month in Pandas
How to Group by Quarter in Pandas
