Multiply each row of one dataframe by all rows of column in second dataframe

Question

I have two dataframes.

Df1

ID #	Date	Units
1821	01/01/22	300
1821	01/02/22	450

Df2

ID #	Hour	% of daily total
1821	0	0.57
1821	1	0.89
1821	2	1.23
1821	3	5.46

I'd like to multiply each row in df1 by all rows in df2. Specifically where both ID #'s match.

Final dataframe units represents the units (300 and 450) from df1 multiplied by the % of daily total ( 0.57%, 0.89%, 1.23%, 5.46%) from df2.

ID #	Date	Hour	Units
1821	01/01/22	0	2
1821	01/01/22	1	3
1821	01/01/22	2	4
1821	01/01/22	3	16
1821	01/02/22	0	3
1821	01/02/22	1	4
1821	01/02/22	2	6
1821	01/02/22	3	25

Thank you for your help

Answer 1

Merge the dataframes on ID #, then pop & multiply the column Units and % of daily total, then divide by 100 and round the get the desired result

df3 = df1.merge(df2, on='ID #', how='left')
df3['Units'] = df3.pop('Units').mul(df3.pop('% of daily total'), fill_value=1).div(100).round()

---

print(df3)

   ID #      Date  Hour  Units
0  1821  01/01/22     0    2.0
1  1821  01/01/22     1    3.0
2  1821  01/01/22     2    4.0
3  1821  01/01/22     3   16.0
4  1821  01/02/22     0    3.0
5  1821  01/02/22     1    4.0
6  1821  01/02/22     2    6.0
7  1821  01/02/22     3   25.0