How can I group by month from a date field using Python and Pandas?

Question

I have a dataframe, df, which is as follows:

| date      | Revenue |
|-----------|---------|
| 6/2/2017  | 100     |
| 5/23/2017 | 200     |
| 5/20/2017 | 300     |
| 6/22/2017 | 400     |
| 6/21/2017 | 500     |

I need to group the above data by month to get output as:

| date | SUM(Revenue) |
|------|--------------|
| May  | 500          |
| June | 1000         |

I tried this code, but it did not work:

df.groupby(month('date')).agg({'Revenue': 'sum'})

I want to only use Pandas or NumPy and no additional libraries.

Answer 1

Try this:

In [6]: df['date'] = pd.to_datetime(df['date'])

In [7]: df
Out[7]:
        date  Revenue
0 2017-06-02      100
1 2017-05-23      200
2 2017-05-20      300
3 2017-06-22      400
4 2017-06-21      500



In [59]: df.groupby(df['date'].dt.strftime('%B'))['Revenue'].sum().sort_values()
Out[59]:
date
May      500
June    1000

Answer 2

Try a groupby using a pandas Grouper:

df = pd.DataFrame({'date':['6/2/2017','5/23/2017','5/20/2017','6/22/2017','6/21/2017'],'Revenue':[100,200,300,400,500]})
df.date = pd.to_datetime(df.date)
dg = df.groupby(pd.Grouper(key='date', freq='1M')).sum() # groupby each 1 month
dg.index = dg.index.strftime('%B')

Output:

     Revenue
 May    500
June    1000

Answer 3

For DataFrame with many rows, using strftime takes up more time. If the date column already has dtype of datetime64[ns] (can use pd.to_datetime() to convert, or specify parse_dates during csv import, etc.), one can directly access datetime property for groupby labels (Method 3). The speedup is substantial.

import numpy as np
import pandas as pd

T = pd.date_range(pd.Timestamp(0), pd.Timestamp.now()).to_frame(index=False)
T = pd.concat([T for i in range(1,10)])
T['revenue'] = pd.Series(np.random.randint(1000, size=T.shape[0]))
T.columns.values[0] = 'date'

print(T.shape) #(159336, 2)
print(T.dtypes) #date: datetime64[ns], revenue: int32

Method 1: strftime

%timeit -n 10 -r 7 T.groupby(T['date'].dt.strftime('%B'))['revenue'].sum()

1.47 s ± 10.1 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

Method 2: Grouper

%timeit -n 10 -r 7 T.groupby(pd.Grouper(key='date', freq='1M')).sum()
#NOTE Manually map months as integer {01..12} to strings

56.9 ms ± 2.88 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

Method 3: datetime properties

%timeit -n 10 -r 7 T.groupby(T['date'].dt.month)['revenue'].sum()
#NOTE Manually map months as integer {01..12} to strings

34 ms ± 3.34 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)

Answer 4

This will work better.

Try this:

# Explicitly convert to date
df['Date'] = pd.to_datetime(df['Date'])
# Set your date column as index 
df.set_index('Date',inplace=True) 

# For monthly use 'M', If needed for other freq you can change.
df[revenue].resample('M').sum()

This code gives the same result as shivsn's answer on the first post.

But the thing is we can do a lot more operations in this mentioned code.

It is recommended to use this:

>>> df['Date'] = pd.to_datetime(df['Date'])
>>> df.set_index('Date',inplace=True)
>>> df['withdrawal'].resample('M').sum().sort_values()
Date
2019-10-31     28710.00
2019-04-30     31437.00
2019-07-31     39728.00
2019-11-30     40121.00
2019-05-31     46495.00
2020-02-29     57751.10
2019-12-31     72469.13
2020-01-31     76115.78
2019-06-30     76947.00
2019-09-30     79847.04
2020-03-31     97920.18
2019-08-31    205279.45
Name: withdrawal, dtype: float64

where shivsn's code does the same.

>>> df.groupby(df['Date'].dt.strftime('%B'))['withdrawal'].sum().sort_values()
Date
October       28710.00
April         31437.00
July          39728.00
November      40121.00
May           46495.00
February      57751.10
December      72469.13
January       76115.78
June          76947.00
September     79847.04
March         97920.18
August       205279.45
Name: withdrawal, dtype: float64

Answer 5

Try this:

1. Change the date column into datetime format.

   ---> df['Date'] = pd.to_datetime(df['Date'])

2. Insert a new row in the data frame which has month like [May, 'June']

   ---> df['months'] = df['date'].apply(lambda x:x.strftime('%B'))

   ---> here x is date which take from date column in data frame.

3. Now aggregate the aggregate data in the month column and sum the revenue.

   --->response_data_frame = df.groupby('months')['Revenue'].sum()

   ---->print(response_data_frame)

Output:

month	Revenue
May	500
June	1000

Answer 6

df['Month'] = pd.DatetimeIndex(df['date']).month_name()

Using this you should get

date	Revenue	Month
6/2/2017	100	June
5/23/2017	200	May
5/20/2017	300	May
6/22/2017	400	June
6/21/2017	500	June