How to subtract two identical dataframes in pandas

Question

I have got two identical dataframes in pandas/python (a and b) only values are different:

a:

date       a1 a2 a3
01.01.2020 2  2  2
02.01.2020 3  3  3
03.01.2020 4  4  4

b:

date       a1 a2 a3
01.01.2020 1  1  1
01.01.2020 2  2  2
01.01.2020 3  3  3

I need a - b and expect to see result c:

date       a1 a2 a3
01.01.2020 1  1  1
01.01.2020 1  1  1
01.01.2020 1  1  1

a - b does not work and I cannot figure out how. Would you please help me? Thanks!

Answer 1

You can set_index :

new_df = (a.set_index('date') - b.set_index('date')).reset_index()

However, that only works if your dates are identical between the two dataframes and different within each.

In the other case (as shown in your sample data) you can do:

c = b.copy()
c.iloc[:,1:] = a.iloc[:, 1:] - b.iloc[:,1:]

Answer 2

Try using df1.subtract(df2) . Simple and elegant.

Answer 3

Assuming that dates in both dataframes are identical, you can use df.sub :

df = a.set_index('date').sub(b.set_index('date')).reset_index()

Output:

         date  a1  a2  a3
0  01.01.2020   1   1   1
1  01.01.2020   1   1   1
2  01.01.2020   1   1   1