.replace works on one row but not column pandas code example

Example 1: replace value of dataframe with another column

df['col1'] = np.where(df['col1'] == 0, df['col2'], df['col1'])
df['col1'] = np.where(df['col1'] == 0, df['col3'], df['col1'])

Example 2: pandas find fifth caracter in field and change cell based on that number

data['result'] = data['result'].map(lambda x: x.lstrip('+-').rstrip('aAbBcC'))