Pandas Dataframe conditional actions

[tom1983]

Hey there,

I have a simple Pandas Dataframe where I want if the condition is met (A is smaller than A of the line above)take the value of C from the line before being the actual value for C:

import pandas as pd
import numpy as np
df = pd.DataFrame({'A' : [1,2,3,4,3,2,1],'B' : [1,2,3,4,3,2,1]})
df['C'] = df['A'] * df['B']
df.loc[df.A < df.A.shift(1), 'C'] = df['C'].shift(1)

print(df)

this gives me:

Output:
   A  B     C
0  1  1   1.0
1  2  2   4.0
2  3  3   9.0
3  4  4  16.0
4  3  3  16.0
5  2  2   9.0
6  1  1   4.0

but what I really want is:

Output:
   A  B     C
0  1  1   1.0
1  2  2   4.0
2  3  3   9.0
3  4  4  16.0
4  3  3  16.0 #A is getting smaller so we use C from the line above
5  2  2  16.0 #A is getting smaller again so we use C from the line above (again 16)
6  1  1  16.0 #A is getting smaller again so we use C from the line above (again 16)

the code I am using is unfortunately not doing what I want, it gives me the value from the line above, but only once.

Any help would be highly appreciated.


Thanks in advance!

Tom

[MAZambelli4353]

df = pd.DataFrame({'A': [1, 2, 3, 4, 3, 2, 1], 'B': [1, 2, 3, 4, 3, 2, 1]})
df['C'] = df['A'] * df['B']

for n in range(len(df['C']) - 1):
    if df['C'][n] > df['C'][n + 1]:
        df['C'][n+1] = df['C'][n]
    else:
        pass
print(df)