Iterate over rows, if statement

Question

I have a dataframe in Python with 4 columns and would like to create a new column based on this Excel condition: =IF(AND(B2=B1;D2=D1;D2=14);1;0). I'm new to Python and am not sure how to start..

Should I create a for loop? If so, how to refer to the previous row?

Answer 1

let df['newCol'] be your new column, the below code should work ('B' and 'D' re the respective column names.

import pandas as pd
import numpy as np 
df = pd.DataFrame({'B': [1,2,2,3], 'D': [2,14,14,4]})
    print(df)

    >>> df
       B   D
    0  1   2
    1  2  14
    2  2  14
    3  3   4

    df['newCol']= [np.NaN]+[1 if (df.loc[i-1,'B']==df.loc[i,'B'] and df.loc[i-1,'d']==df.loc[i,'D'] and df.loc[i,'D']==14) else 0 for i in range(1,len(df))]
    print(df)

    >>> df
       B   D  newCol
    0  1   2  NaN
    1  2  14  0.0
    2  2  14  1.0
    3  3   4  0.0