Python Pandas - how to add columns of filtered sum and calculate percentage weight

Question

I would like to add two columns to a pandas df to show daily totals and weights. Existing df:

Date	Name	Value
2022-2-1	Apple	5
2022-2-1	Pear	3
2022-2-2	Apple	4
2022-2-2	Pear	4
2022-2-2	Banana	2
2022-2-3	Apple	5
2022-2-3	Banana	3
2022-2-4	Apple	4
2022-2-4	Banana	2
2022-2-4	Papaya	9

Desired output:

Date	Name	Value	Daily Total	Percentage Weight
2022-2-1	Apple	5	8	62.5%
2022-2-1	Pear	3	8	37.5%
2022-2-2	Apple	4	10	40%
2022-2-2	Pear	4	10	40%
2022-2-2	Banana	2	10	20%
2022-2-3	Apple	5	8	62.5%
2022-2-3	Banana	3	8	37.5%
2022-2-4	Apple	4	15	26.7%
2022-2-4	Banana	2	15	13.3%
2022-2-4	Papaya	9	15	60%

Appreciate any ideas/suggestions.

Answer 1

Use groupby + transform('sum') :

df['Daily Total'] = df.groupby('Date')['Value'].transform('sum')
df['Percentage Weight'] = (df['Value'] / df['Daily Total'] * 100).round(1).map('{}%'.format)

Output:

>>> df
       Date    Name  Value  Daily Total Percentage Weight
0  2022-2-1   Apple      5            8             62.5%
1  2022-2-1    Pear      3            8             37.5%
2  2022-2-2   Apple      4           10             40.0%
3  2022-2-2    Pear      4           10             40.0%
4  2022-2-2  Banana      2           10             20.0%
5  2022-2-3   Apple      5            8             62.5%
6  2022-2-3  Banana      3            8             37.5%
7  2022-2-4   Apple      4           15             26.7%
8  2022-2-4  Banana      2           15             13.3%
9  2022-2-4  Papaya      9           15             60.0%

One-liner:

df = df.assign(DailyTotal=df.groupby('Date')['Value'].transform('sum')).pipe(lambda x: x.assign(PercentageWeight=df['Value'].div(df['Daily Total']).mul(100).round(1).map('{}%'.format)))