How to use functions with pandas dataframe

Question

How can I use function with pandas dataframe. For example:

a       | b
london  | uk
newyork | usa
berlin  | germany

df1 = df[[\'a\', \'b\']]

def doSomething(df         


        

Answer 1

df1 = df[['a', 'b']]

def doSomething(df):
df2 = df['a']
return df2

df3 = df1.apply(doSomething, axis=1)
df3 = pd.DataFrame(df3).rename(columns={0: 'a'})