我如何获取两个列表 Pandas DataFrame 列名，并且只使用一个列表，但 append 一个循环中的字符串应用于列名？

Question

I have two separate DataFrames:

df_a
df_b

The column names, type of data, and length are identical but the numbers are different. I want to subtract (df_a - df_b) and record that number in a new dataframe df_dif. I can manage that okay with what I have below:

colnames_in = ['col a', 'col b', 'col c']
colnames_out = ['new col a', 'new col b', 'new col c']

    for i in range(len(colnames_in)):
        df_dif[colnames_out[i] = df_a[colnames_in[i]] - df_b[colnames_in[i]]

Where I am stuck is trying to be less repetitious. How would i accomplish the same, but instead of listing out colnames_out as a list...just append the string 'new'?

Answer 1

i think this should work:

df_new = df_a.copy()
df_new.subtract(df_b)

Answer 2

IIUC, you can use pandas.add_prefix for that:

colnames_in = ['col a', 'col b', 'col c']

df_a = pd.DataFrame([[10, 20, 30], [40, 50, 60], [70, 80, 90]], columns=colnames_in)
df_b = pd.DataFrame([[1, 2, 3], [4, 5, 6], [7, 8, 9]], columns=colnames_in)

df_diff = df_a.subtract(df_b).add_prefix('new ')

Output:

   new col a  new col b  new col c
0          9         18         27
1         36         45         54
2         63         72         81